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 $49.35   4.115%   $51.3808   $51.38   $51.40   $51.40  
  Purchase #2 $113.78   9.810%   $124.9418   $124.94   $124.95   $124.90  
  Purchase #3 $237.53   12.303%   $266.7533   $266.75   $266.75   $266.80  
  Purchase #4 $148.50   8.812%   $161.5858   $161.59   $161.60   $161.60  
  Purchase #5 $83.49   5.699%   $88.2481   $88.25   $88.25   $88.20  
  Purchase #6 $238.74   8.277%   $258.5005   $258.50   $258.50   $258.50  
  Purchase #7 $126.37   12.442%   $142.093   $142.09   $142.10   $142.10  
  7 purchase totals = $997.76       $1,093.5033   $1,093.50   $1,093.55   $1,093.50