Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $144.67   6.281%   $153.7567   $153.76   $153.75   $153.80  
  Purchase #2 $96.33   12.140%   $108.0245   $108.02   $108.00   $108.00  
  Purchase #3 $138.95   12.190%   $155.888   $155.89   $155.90   $155.90  
  Purchase #4 $227.38   3.562%   $235.4793   $235.48   $235.50   $235.50  
  Purchase #5 $108.75   6.786%   $116.1298   $116.13   $116.15   $116.10  
  Purchase #6 $134.74   10.586%   $149.0036   $149.00   $149.00   $149.00  
  Purchase #7 $128.37   10.859%   $142.3097   $142.31   $142.30   $142.30  
  7 purchase totals = $979.19       $1,060.5916   $1,060.59   $1,060.60   $1,060.60