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 $244.51   11.659%   $273.0174   $273.02   $273.00   $273.00  
  Purchase #2 $23.99   6.472%   $25.5426   $25.54   $25.55   $25.50  
  Purchase #3 $150.34   7.609%   $161.7794   $161.78   $161.80   $161.80  
  Purchase #4 $163.39   9.609%   $179.0901   $179.09   $179.10   $179.10  
  Purchase #5 $174.55   6.234%   $185.4314   $185.43   $185.45   $185.40  
  Purchase #6 $239.72   11.822%   $268.0597   $268.06   $268.05   $268.10  
  Purchase #7 $229.61   11.113%   $255.1266   $255.13   $255.15   $255.10  
  7 purchase totals = $1,226.11       $1,348.0472   $1,348.05   $1,348.10   $1,348.00