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 $141.31   5.577%   $149.1909   $149.19   $149.20   $149.20  
  Purchase #2 $201.27   11.171%   $223.7539   $223.75   $223.75   $223.80  
  Purchase #3 $215.57   5.703%   $227.864   $227.86   $227.85   $227.90  
  Purchase #4 $88.88   7.237%   $95.3122   $95.31   $95.30   $95.30  
  Purchase #5 $41.52   3.651%   $43.0359   $43.04   $43.05   $43.00  
  Purchase #6 $46.79   13.285%   $53.0061   $53.01   $53.00   $53.00  
  Purchase #7 $26.29   9.163%   $28.699   $28.70   $28.70   $28.70  
  7 purchase totals = $761.63       $820.8620   $820.86   $820.85   $820.90