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 $214.98   6.171%   $228.2464   $228.25   $228.25   $228.20  
  Purchase #2 $55.39   4.571%   $57.9219   $57.92   $57.90   $57.90  
  Purchase #3 $41.25   11.418%   $45.9599   $45.96   $45.95   $46.00  
  Purchase #4 $58.69   9.460%   $64.2421   $64.24   $64.25   $64.20  
  Purchase #5 $66.43   11.837%   $74.2933   $74.29   $74.30   $74.30  
  Purchase #6 $79.93   11.282%   $88.9477   $88.95   $88.95   $88.90  
  Purchase #7 $106.74   11.568%   $119.0877   $119.09   $119.10   $119.10  
  7 purchase totals = $623.41       $678.6990   $678.70   $678.70   $678.60