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 $236.56   10.202%   $260.6939   $260.69   $260.70   $260.70  
  Purchase #2 $214.58   13.524%   $243.5998   $243.60   $243.60   $243.60  
  Purchase #3 $119.55   10.431%   $132.0203   $132.02   $132.00   $132.00  
  Purchase #4 $232.97   13.825%   $265.1781   $265.18   $265.20   $265.20  
  Purchase #5 $20.62   9.633%   $22.6063   $22.61   $22.60   $22.60  
  Purchase #6 $50.97   8.751%   $55.4304   $55.43   $55.45   $55.40  
  Purchase #7 $229.52   9.536%   $251.407   $251.41   $251.40   $251.40  
  7 purchase totals = $1,104.77       $1,230.9358   $1,230.94   $1,230.95   $1,230.90