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 $38.98   12.194%   $43.7332   $43.73   $43.75   $43.70  
  Purchase #2 $129.70   9.215%   $141.6519   $141.65   $141.65   $141.70  
  Purchase #3 $119.96   4.413%   $125.2538   $125.25   $125.25   $125.30  
  Purchase #4 $149.37   6.751%   $159.454   $159.45   $159.45   $159.50  
  Purchase #5 $154.41   9.709%   $169.4017   $169.40   $169.40   $169.40  
  Purchase #6 $144.89   12.736%   $163.3432   $163.34   $163.35   $163.30  
  Purchase #7 $178.60   13.823%   $203.2879   $203.29   $203.30   $203.30  
  7 purchase totals = $915.91       $1,006.1257   $1,006.11   $1,006.15   $1,006.20