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 $60.88   11.826%   $68.0797   $68.08   $68.10   $68.10  
  Purchase #2 $96.80   7.763%   $104.3146   $104.31   $104.30   $104.30  
  Purchase #3 $215.66   6.394%   $229.4493   $229.45   $229.45   $229.40  
  Purchase #4 $53.85   10.601%   $59.5586   $59.56   $59.55   $59.60  
  Purchase #5 $213.42   3.727%   $221.3742   $221.37   $221.35   $221.40  
  Purchase #6 $111.29   12.576%   $125.2858   $125.29   $125.30   $125.30  
  Purchase #7 $75.67   13.212%   $85.6675   $85.67   $85.65   $85.70  
  7 purchase totals = $827.57       $893.7297   $893.73   $893.70   $893.80