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 $151.97   9.763%   $166.8068   $166.81   $166.80   $166.80  
  Purchase #2 $116.72   10.371%   $128.825   $128.83   $128.85   $128.80  
  Purchase #3 $153.68   10.669%   $170.0761   $170.08   $170.10   $170.10  
  Purchase #4 $186.75   8.629%   $202.8647   $202.86   $202.85   $202.90  
  Purchase #5 $116.29   8.339%   $125.9874   $125.99   $126.00   $126.00  
  Purchase #6 $186.71   10.349%   $206.0326   $206.03   $206.05   $206.00  
  Purchase #7 $41.29   7.427%   $44.3566   $44.36   $44.35   $44.40  
  7 purchase totals = $953.41       $1,044.9492   $1,044.96   $1,045.00   $1,045.00