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 $83.52   10.616%   $92.3865   $92.39   $92.40   $92.40  
  Purchase #2 $91.91   13.837%   $104.6276   $104.63   $104.65   $104.60  
  Purchase #3 $173.62   8.163%   $187.7926   $187.79   $187.80   $187.80  
  Purchase #4 $191.42   13.638%   $217.5259   $217.53   $217.55   $217.50  
  Purchase #5 $45.29   8.276%   $49.0382   $49.04   $49.05   $49.00  
  Purchase #6 $152.42   12.593%   $171.6143   $171.61   $171.60   $171.60  
  Purchase #7 $214.58   13.745%   $244.074   $244.07   $244.05   $244.10  
  7 purchase totals = $952.76       $1,067.0591   $1,067.06   $1,067.10   $1,067.00