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 $87.85   10.713%   $97.2614   $97.26   $97.25   $97.30  
  Purchase #2 $102.95   4.818%   $107.9101   $107.91   $107.90   $107.90  
  Purchase #3 $215.84   11.451%   $240.5558   $240.56   $240.55   $240.60  
  Purchase #4 $141.78   12.783%   $159.9037   $159.90   $159.90   $159.90  
  Purchase #5 $128.64   9.507%   $140.8698   $140.87   $140.85   $140.90  
  Purchase #6 $113.77   5.455%   $119.9762   $119.98   $120.00   $120.00  
  Purchase #7 $99.52   5.103%   $104.5985   $104.60   $104.60   $104.60  
  7 purchase totals = $890.35       $971.0755   $971.08   $971.05   $971.20