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 $119.50   11.466%   $133.2019   $133.20   $133.20   $133.20  
  Purchase #2 $13.43   9.629%   $14.7232   $14.72   $14.70   $14.70  
  Purchase #3 $116.50   8.201%   $126.0542   $126.05   $126.05   $126.10  
  Purchase #4 $93.64   13.844%   $106.6035   $106.60   $106.60   $106.60  
  Purchase #5 $43.88   10.179%   $48.3465   $48.35   $48.35   $48.30  
  Purchase #6 $178.45   12.657%   $201.0364   $201.04   $201.05   $201.00  
  Purchase #7 $50.81   5.688%   $53.7001   $53.70   $53.70   $53.70  
  7 purchase totals = $616.21       $683.6658   $683.66   $683.65   $683.60