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 $64.30   6.307%   $68.3554   $68.36   $68.35   $68.40  
  Purchase #2 $203.93   13.454%   $231.3667   $231.37   $231.35   $231.40  
  Purchase #3 $109.78   12.269%   $123.2489   $123.25   $123.25   $123.20  
  Purchase #4 $207.58   7.254%   $222.6379   $222.64   $222.65   $222.60  
  Purchase #5 $173.82   12.340%   $195.2694   $195.27   $195.25   $195.30  
  Purchase #6 $197.33   3.156%   $203.5577   $203.56   $203.55   $203.60  
  Purchase #7 $106.44   10.409%   $117.5193   $117.52   $117.50   $117.50  
  7 purchase totals = $1,063.18       $1,161.9553   $1,161.97   $1,161.90   $1,162.00