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 $37.42   8.282%   $40.5191   $40.52   $40.50   $40.50  
  Purchase #2 $194.93   4.292%   $203.2964   $203.30   $203.30   $203.30  
  Purchase #3 $187.61   9.513%   $205.4573   $205.46   $205.45   $205.50  
  Purchase #4 $211.44   9.596%   $231.7298   $231.73   $231.75   $231.70  
  Purchase #5 $126.56   6.270%   $134.4953   $134.50   $134.50   $134.50  
  Purchase #6 $53.38   13.444%   $60.5564   $60.56   $60.55   $60.60  
  Purchase #7 $23.56   11.699%   $26.3163   $26.32   $26.30   $26.30  
  7 purchase totals = $834.90       $902.3706   $902.39   $902.35   $902.40