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 $229.58   8.609%   $249.3445   $249.34   $249.35   $249.30  
  Purchase #2 $242.98   12.446%   $273.2213   $273.22   $273.20   $273.20  
  Purchase #3 $43.55   5.586%   $45.9827   $45.98   $46.00   $46.00  
  Purchase #4 $222.27   9.807%   $244.068   $244.07   $244.05   $244.10  
  Purchase #5 $67.77   8.639%   $73.6247   $73.62   $73.60   $73.60  
  Purchase #6 $221.37   3.246%   $228.5557   $228.56   $228.55   $228.60  
  Purchase #7 $120.72   5.714%   $127.6179   $127.62   $127.60   $127.60  
  7 purchase totals = $1,148.24       $1,242.4148   $1,242.41   $1,242.35   $1,242.40