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 $235.71   5.245%   $248.073   $248.07   $248.05   $248.10  
  Purchase #2 $33.36   13.134%   $37.7415   $37.74   $37.75   $37.70  
  Purchase #3 $231.94   13.293%   $262.7718   $262.77   $262.75   $262.80  
  Purchase #4 $146.57   9.523%   $160.5279   $160.53   $160.55   $160.50  
  Purchase #5 $151.74   13.814%   $172.7014   $172.70   $172.70   $172.70  
  Purchase #6 $151.32   11.679%   $168.9927   $168.99   $169.00   $169.00  
  Purchase #7 $188.94   5.702%   $199.7134   $199.71   $199.70   $199.70  
  7 purchase totals = $1,139.58       $1,250.5217   $1,250.51   $1,250.50   $1,250.50