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 $83.95   9.457%   $91.8892   $91.89   $91.90   $91.90  
  Purchase #2 $111.56   12.649%   $125.6712   $125.67   $125.65   $125.70  
  Purchase #3 $160.79   5.132%   $169.0417   $169.04   $169.05   $169.00  
  Purchase #4 $66.29   10.614%   $73.326   $73.33   $73.35   $73.30  
  Purchase #5 $18.60   11.505%   $20.7399   $20.74   $20.75   $20.70  
  Purchase #6 $125.99   6.672%   $134.3961   $134.40   $134.40   $134.40  
  Purchase #7 $102.58   7.159%   $109.9237   $109.92   $109.90   $109.90  
  7 purchase totals = $669.76       $724.9878   $724.99   $725.00   $724.90