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 $97.66   5.766%   $103.2911   $103.29   $103.30   $103.30  
  Purchase #2 $217.33   8.112%   $234.9598   $234.96   $234.95   $235.00  
  Purchase #3 $48.48   5.265%   $51.0325   $51.03   $51.05   $51.00  
  Purchase #4 $213.31   4.585%   $223.0903   $223.09   $223.10   $223.10  
  Purchase #5 $176.44   9.394%   $193.0148   $193.01   $193.00   $193.00  
  Purchase #6 $86.81   12.278%   $97.4685   $97.47   $97.45   $97.50  
  Purchase #7 $219.45   4.166%   $228.5923   $228.59   $228.60   $228.60  
  7 purchase totals = $1,059.48       $1,131.4493   $1,131.44   $1,131.45   $1,131.50