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 $55.79   9.461%   $61.0683   $61.07   $61.05   $61.10  
  Purchase #2 $62.25   6.419%   $66.2458   $66.25   $66.25   $66.20  
  Purchase #3 $211.39   5.709%   $223.4583   $223.46   $223.45   $223.50  
  Purchase #4 $25.80   9.292%   $28.1973   $28.20   $28.20   $28.20  
  Purchase #5 $17.80   8.745%   $19.3566   $19.36   $19.35   $19.40  
  Purchase #6 $178.44   3.839%   $185.2903   $185.29   $185.30   $185.30  
  Purchase #7 $110.90   5.841%   $117.3777   $117.38   $117.40   $117.40  
  7 purchase totals = $662.37       $700.9943   $701.01   $701.00   $701.10