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 $44.88   8.344%   $48.6248   $48.62   $48.60   $48.60  
  Purchase #2 $170.84   10.140%   $188.1632   $188.16   $188.15   $188.20  
  Purchase #3 $229.32   12.560%   $258.1226   $258.12   $258.10   $258.10  
  Purchase #4 $210.25   13.190%   $237.982   $237.98   $238.00   $238.00  
  Purchase #5 $117.52   6.184%   $124.7874   $124.79   $124.80   $124.80  
  Purchase #6 $102.92   13.174%   $116.4787   $116.48   $116.50   $116.50  
  Purchase #7 $121.35   8.513%   $131.6805   $131.68   $131.70   $131.70  
  7 purchase totals = $997.08       $1,105.8392   $1,105.83   $1,105.85   $1,105.90