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 $76.46   10.854%   $84.759   $84.76   $84.75   $84.80  
  Purchase #2 $69.39   4.604%   $72.5847   $72.58   $72.60   $72.60  
  Purchase #3 $87.62   4.126%   $91.2352   $91.24   $91.25   $91.20  
  Purchase #4 $229.78   10.300%   $253.4473   $253.45   $253.45   $253.40  
  Purchase #5 $162.26   6.742%   $173.1996   $173.20   $173.20   $173.20  
  Purchase #6 $225.29   6.612%   $240.1862   $240.19   $240.20   $240.20  
  Purchase #7 $119.56   13.373%   $135.5488   $135.55   $135.55   $135.50  
  7 purchase totals = $970.36       $1,050.9608   $1,050.97   $1,051.00   $1,050.90