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 $70.34   7.604%   $75.6887   $75.69   $75.70   $75.70  
  Purchase #2 $181.65   11.874%   $203.2191   $203.22   $203.20   $203.20  
  Purchase #3 $111.94   5.192%   $117.7519   $117.75   $117.75   $117.80  
  Purchase #4 $84.31   11.167%   $93.7249   $93.72   $93.70   $93.70  
  Purchase #5 $55.29   8.549%   $60.0167   $60.02   $60.00   $60.00  
  Purchase #6 $236.34   3.324%   $244.1959   $244.20   $244.20   $244.20  
  Purchase #7 $165.41   8.222%   $179.01   $179.01   $179.00   $179.00  
  7 purchase totals = $905.28       $973.6072   $973.61   $973.55   $973.60