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 $226.33   11.476%   $252.3036   $252.30   $252.30   $252.30  
  Purchase #2 $203.56   7.193%   $218.2021   $218.20   $218.20   $218.20  
  Purchase #3 $89.54   3.223%   $92.4259   $92.43   $92.45   $92.40  
  Purchase #4 $13.81   3.768%   $14.3304   $14.33   $14.35   $14.30  
  Purchase #5 $133.31   13.370%   $151.1335   $151.13   $151.15   $151.10  
  Purchase #6 $24.37   6.151%   $25.869   $25.87   $25.85   $25.90  
  Purchase #7 $250.58   5.460%   $264.2617   $264.26   $264.25   $264.30  
  7 purchase totals = $941.50       $1,018.5262   $1,018.52   $1,018.55   $1,018.50