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 $54.96   11.204%   $61.1177   $61.12   $61.10   $61.10  
  Purchase #2 $99.44   3.516%   $102.9363   $102.94   $102.95   $102.90  
  Purchase #3 $218.87   5.819%   $231.606   $231.61   $231.60   $231.60  
  Purchase #4 $189.76   10.779%   $210.2142   $210.21   $210.20   $210.20  
  Purchase #5 $169.30   9.334%   $185.1025   $185.10   $185.10   $185.10  
  Purchase #6 $208.80   5.517%   $220.3195   $220.32   $220.30   $220.30  
  Purchase #7 $191.48   9.454%   $209.5825   $209.58   $209.60   $209.60  
  7 purchase totals = $1,132.61       $1,220.8787   $1,220.88   $1,220.85   $1,220.80