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 $146.68   13.462%   $166.4261   $166.43   $166.45   $166.40  
  Purchase #2 $125.73   4.783%   $131.7437   $131.74   $131.75   $131.70  
  Purchase #3 $167.92   4.714%   $175.8357   $175.84   $175.85   $175.80  
  Purchase #4 $207.68   10.190%   $228.8426   $228.84   $228.85   $228.80  
  Purchase #5 $235.53   3.379%   $243.4886   $243.49   $243.50   $243.50  
  Purchase #6 $244.42   11.810%   $273.286   $273.29   $273.30   $273.30  
  Purchase #7 $23.27   7.461%   $25.0062   $25.01   $25.00   $25.00  
  7 purchase totals = $1,151.23       $1,244.6289   $1,244.64   $1,244.70   $1,244.50