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 $79.86   10.494%   $88.2405   $88.24   $88.25   $88.20  
  Purchase #2 $61.92   5.258%   $65.1758   $65.18   $65.20   $65.20  
  Purchase #3 $100.70   10.164%   $110.9351   $110.94   $110.95   $110.90  
  Purchase #4 $132.58   9.741%   $145.4946   $145.49   $145.50   $145.50  
  Purchase #5 $162.78   11.619%   $181.6934   $181.69   $181.70   $181.70  
  Purchase #6 $200.26   13.850%   $227.996   $228.00   $228.00   $228.00  
  Purchase #7 $96.27   7.708%   $103.6905   $103.69   $103.70   $103.70  
  7 purchase totals = $834.37       $923.2259   $923.23   $923.30   $923.20