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 $90.94   6.163%   $96.5446   $96.54   $96.55   $96.50  
  Purchase #2 $80.64   4.359%   $84.1551   $84.16   $84.15   $84.20  
  Purchase #3 $238.29   11.347%   $265.3288   $265.33   $265.35   $265.30  
  Purchase #4 $65.97   3.142%   $68.0428   $68.04   $68.05   $68.00  
  Purchase #5 $38.71   7.255%   $41.5184   $41.52   $41.50   $41.50  
  Purchase #6 $230.91   11.680%   $257.8803   $257.88   $257.90   $257.90  
  Purchase #7 $219.42   6.653%   $234.018   $234.02   $234.00   $234.00  
  7 purchase totals = $964.88       $1,047.4880   $1,047.49   $1,047.50   $1,047.40