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 $177.73   13.643%   $201.9777   $201.98   $202.00   $202.00  
  Purchase #2 $132.80   5.158%   $139.6498   $139.65   $139.65   $139.60  
  Purchase #3 $64.64   7.245%   $69.3232   $69.32   $69.30   $69.30  
  Purchase #4 $21.75   10.160%   $23.9598   $23.96   $23.95   $24.00  
  Purchase #5 $25.35   12.645%   $28.5555   $28.56   $28.55   $28.60  
  Purchase #6 $59.72   3.167%   $61.6113   $61.61   $61.60   $61.60  
  Purchase #7 $175.79   4.669%   $183.9976   $184.00   $184.00   $184.00  
  7 purchase totals = $657.78       $709.0749   $709.08   $709.05   $709.10