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 $95.38   8.722%   $103.699   $103.70   $103.70   $103.70  
  Purchase #2 $81.82   7.199%   $87.7102   $87.71   $87.70   $87.70  
  Purchase #3 $125.96   12.207%   $141.3359   $141.34   $141.35   $141.30  
  Purchase #4 $149.49   11.592%   $166.8189   $166.82   $166.80   $166.80  
  Purchase #5 $52.64   13.229%   $59.6037   $59.60   $59.60   $59.60  
  Purchase #6 $118.84   13.583%   $134.982   $134.98   $135.00   $135.00  
  Purchase #7 $75.65   9.166%   $82.5841   $82.58   $82.60   $82.60  
  7 purchase totals = $699.78       $776.7338   $776.73   $776.75   $776.70