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 $88.79   9.614%   $97.3263   $97.33   $97.35   $97.30  
  Purchase #2 $177.31   4.237%   $184.8226   $184.82   $184.80   $184.80  
  Purchase #3 $102.46   12.538%   $115.3064   $115.31   $115.30   $115.30  
  Purchase #4 $145.43   10.106%   $160.1272   $160.13   $160.15   $160.10  
  Purchase #5 $150.45   10.725%   $166.5858   $166.59   $166.60   $166.60  
  Purchase #6 $202.51   6.609%   $215.8939   $215.89   $215.90   $215.90  
  Purchase #7 $234.25   8.578%   $254.344   $254.34   $254.35   $254.30  
  7 purchase totals = $1,101.20       $1,194.4062   $1,194.41   $1,194.45   $1,194.30