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 $211.78   5.300%   $223.0043   $223.00   $223.00   $223.00  
  Purchase #2 $103.35   12.261%   $116.0217   $116.02   $116.00   $116.00  
  Purchase #3 $42.79   4.620%   $44.7669   $44.77   $44.75   $44.80  
  Purchase #4 $167.89   7.656%   $180.7437   $180.74   $180.75   $180.70  
  Purchase #5 $234.35   5.247%   $246.6463   $246.65   $246.65   $246.60  
  Purchase #6 $100.81   5.579%   $106.4342   $106.43   $106.45   $106.40  
  Purchase #7 $87.71   7.497%   $94.2856   $94.29   $94.30   $94.30  
  7 purchase totals = $948.68       $1,011.9027   $1,011.90   $1,011.90   $1,011.80