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 $66.51   12.396%   $74.7546   $74.75   $74.75   $74.80  
  Purchase #2 $211.89   13.766%   $241.0588   $241.06   $241.05   $241.10  
  Purchase #3 $172.79   12.225%   $193.9136   $193.91   $193.90   $193.90  
  Purchase #4 $15.27   12.611%   $17.1957   $17.20   $17.20   $17.20  
  Purchase #5 $161.70   11.585%   $180.4329   $180.43   $180.45   $180.40  
  Purchase #6 $106.35   7.134%   $113.937   $113.94   $113.95   $113.90  
  Purchase #7 $67.98   7.474%   $73.0608   $73.06   $73.05   $73.10  
  7 purchase totals = $802.49       $894.3534   $894.35   $894.35   $894.40