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 $80.57   13.860%   $91.737   $91.74   $91.75   $91.70  
  Purchase #2 $162.50   8.106%   $175.6723   $175.67   $175.65   $175.70  
  Purchase #3 $207.98   4.233%   $216.7838   $216.78   $216.80   $216.80  
  Purchase #4 $184.85   4.777%   $193.6803   $193.68   $193.70   $193.70  
  Purchase #5 $118.55   11.830%   $132.5745   $132.57   $132.55   $132.60  
  Purchase #6 $237.41   5.224%   $249.8123   $249.81   $249.80   $249.80  
  Purchase #7 $79.33   12.624%   $89.3446   $89.34   $89.35   $89.30  
  7 purchase totals = $1,071.19       $1,149.6048   $1,149.59   $1,149.60   $1,149.60