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 $211.47   11.471%   $235.7277   $235.73   $235.75   $235.70  
  Purchase #2 $137.53   13.258%   $155.7637   $155.76   $155.75   $155.80  
  Purchase #3 $241.58   13.825%   $274.9784   $274.98   $275.00   $275.00  
  Purchase #4 $39.83   7.816%   $42.9431   $42.94   $42.95   $42.90  
  Purchase #5 $105.66   4.127%   $110.0206   $110.02   $110.00   $110.00  
  Purchase #6 $213.82   9.272%   $233.6454   $233.65   $233.65   $233.60  
  Purchase #7 $160.26   11.299%   $178.3678   $178.37   $178.35   $178.40  
  7 purchase totals = $1,110.15       $1,231.4467   $1,231.45   $1,231.45   $1,231.40