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 $48.77   12.689%   $54.9584   $54.96   $54.95   $55.00  
  Purchase #2 $161.37   12.283%   $181.1911   $181.19   $181.20   $181.20  
  Purchase #3 $243.65   11.591%   $271.8915   $271.89   $271.90   $271.90  
  Purchase #4 $121.68   8.490%   $132.0106   $132.01   $132.00   $132.00  
  Purchase #5 $208.31   9.167%   $227.4058   $227.41   $227.40   $227.40  
  Purchase #6 $193.87   11.780%   $216.7079   $216.71   $216.70   $216.70  
  Purchase #7 $190.72   10.564%   $210.8677   $210.87   $210.85   $210.90  
  7 purchase totals = $1,168.37       $1,295.0330   $1,295.04   $1,295.00   $1,295.10