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 $167.97   12.129%   $188.3431   $188.34   $188.35   $188.30  
  Purchase #2 $54.74   8.445%   $59.3628   $59.36   $59.35   $59.40  
  Purchase #3 $29.47   8.497%   $31.9741   $31.97   $31.95   $32.00  
  Purchase #4 $58.85   10.197%   $64.8509   $64.85   $64.85   $64.90  
  Purchase #5 $196.86   11.291%   $219.0875   $219.09   $219.10   $219.10  
  Purchase #6 $182.78   13.572%   $207.5869   $207.59   $207.60   $207.60  
  Purchase #7 $169.54   7.325%   $181.9588   $181.96   $181.95   $182.00  
  7 purchase totals = $860.21       $953.1641   $953.16   $953.15   $953.30