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 $32.91   13.131%   $37.2314   $37.23   $37.25   $37.20  
  Purchase #2 $241.93   10.219%   $266.6528   $266.65   $266.65   $266.70  
  Purchase #3 $212.82   6.370%   $226.3766   $226.38   $226.40   $226.40  
  Purchase #4 $12.82   11.440%   $14.2866   $14.29   $14.30   $14.30  
  Purchase #5 $237.58   7.363%   $255.073   $255.07   $255.05   $255.10  
  Purchase #6 $181.99   12.777%   $205.2429   $205.24   $205.25   $205.20  
  Purchase #7 $222.85   9.250%   $243.4636   $243.46   $243.45   $243.50  
  7 purchase totals = $1,142.90       $1,248.3269   $1,248.32   $1,248.35   $1,248.40