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 $113.33   4.402%   $118.3188   $118.32   $118.30   $118.30  
  Purchase #2 $137.75   12.257%   $154.634   $154.63   $154.65   $154.60  
  Purchase #3 $123.94   4.709%   $129.7763   $129.78   $129.80   $129.80  
  Purchase #4 $97.52   9.706%   $106.9853   $106.99   $107.00   $107.00  
  Purchase #5 $9.52   11.758%   $10.6394   $10.64   $10.65   $10.60  
  Purchase #6 $80.60   11.325%   $89.728   $89.73   $89.75   $89.70  
  Purchase #7 $42.76   9.753%   $46.9304   $46.93   $46.95   $46.90  
  7 purchase totals = $605.42       $657.0122   $657.02   $657.10   $656.90