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 $154.48   9.412%   $169.0197   $169.02   $169.00   $169.00  
  Purchase #2 $85.41   3.269%   $88.2021   $88.20   $88.20   $88.20  
  Purchase #3 $195.26   12.650%   $219.9604   $219.96   $219.95   $220.00  
  Purchase #4 $228.82   13.624%   $259.9944   $259.99   $260.00   $260.00  
  Purchase #5 $205.43   13.276%   $232.7029   $232.70   $232.70   $232.70  
  Purchase #6 $105.70   6.146%   $112.1963   $112.20   $112.20   $112.20  
  Purchase #7 $223.37   4.192%   $232.7337   $232.73   $232.75   $232.70  
  7 purchase totals = $1,198.47       $1,314.8095   $1,314.80   $1,314.80   $1,314.80