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 $59.67   7.566%   $64.1846   $64.18   $64.20   $64.20  
  Purchase #2 $209.85   11.772%   $234.5535   $234.55   $234.55   $234.60  
  Purchase #3 $157.78   13.666%   $179.3422   $179.34   $179.35   $179.30  
  Purchase #4 $121.44   8.696%   $132.0004   $132.00   $132.00   $132.00  
  Purchase #5 $62.53   8.375%   $67.7669   $67.77   $67.75   $67.80  
  Purchase #6 $218.66   11.363%   $243.5063   $243.51   $243.50   $243.50  
  Purchase #7 $249.33   4.256%   $259.9415   $259.94   $259.95   $259.90  
  7 purchase totals = $1,079.26       $1,181.2954   $1,181.29   $1,181.30   $1,181.30