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 $105.29   13.820%   $119.8411   $119.84   $119.85   $119.80  
  Purchase #2 $105.62   10.352%   $116.5538   $116.55   $116.55   $116.60  
  Purchase #3 $23.99   12.768%   $27.053   $27.05   $27.05   $27.10  
  Purchase #4 $226.78   8.782%   $246.6958   $246.70   $246.70   $246.70  
  Purchase #5 $85.35   13.161%   $96.5829   $96.58   $96.60   $96.60  
  Purchase #6 $94.85   10.477%   $104.7874   $104.79   $104.80   $104.80  
  Purchase #7 $135.44   12.562%   $152.454   $152.45   $152.45   $152.50  
  7 purchase totals = $777.32       $863.9680   $863.96   $864.00   $864.10