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 $229.88   11.210%   $255.6495   $255.65   $255.65   $255.60  
  Purchase #2 $166.98   4.325%   $174.2019   $174.20   $174.20   $174.20  
  Purchase #3 $48.59   11.165%   $54.0151   $54.02   $54.00   $54.00  
  Purchase #4 $53.26   13.247%   $60.3154   $60.32   $60.30   $60.30  
  Purchase #5 $101.43   3.701%   $105.1839   $105.18   $105.20   $105.20  
  Purchase #6 $182.82   4.421%   $190.9025   $190.90   $190.90   $190.90  
  Purchase #7 $207.28   5.765%   $219.2297   $219.23   $219.25   $219.20  
  7 purchase totals = $990.24       $1,059.4980   $1,059.50   $1,059.50   $1,059.40