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 $52.75   11.855%   $59.0035   $59.00   $59.00   $59.00  
  Purchase #2 $229.36   12.815%   $258.7525   $258.75   $258.75   $258.80  
  Purchase #3 $35.44   7.343%   $38.0424   $38.04   $38.05   $38.00  
  Purchase #4 $145.74   9.456%   $159.5212   $159.52   $159.50   $159.50  
  Purchase #5 $142.88   5.281%   $150.4255   $150.43   $150.45   $150.40  
  Purchase #6 $242.66   13.294%   $274.9192   $274.92   $274.90   $274.90  
  Purchase #7 $116.49   11.346%   $129.707   $129.71   $129.70   $129.70  
  7 purchase totals = $965.32       $1,070.3713   $1,070.37   $1,070.35   $1,070.30