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 $100.73   10.274%   $111.079   $111.08   $111.10   $111.10  
  Purchase #2 $216.77   11.333%   $241.3365   $241.34   $241.35   $241.30  
  Purchase #3 $128.97   13.391%   $146.2404   $146.24   $146.25   $146.20  
  Purchase #4 $209.92   3.454%   $217.1706   $217.17   $217.15   $217.20  
  Purchase #5 $170.99   13.759%   $194.5165   $194.52   $194.50   $194.50  
  Purchase #6 $247.67   5.790%   $262.0101   $262.01   $262.00   $262.00  
  Purchase #7 $95.60   4.234%   $99.6477   $99.65   $99.65   $99.60  
  7 purchase totals = $1,170.65       $1,272.0008   $1,272.01   $1,272.00   $1,271.90