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 $77.32   9.462%   $84.636   $84.64   $84.65   $84.60  
  Purchase #2 $214.92   13.286%   $243.4743   $243.47   $243.45   $243.50  
  Purchase #3 $75.84   11.765%   $84.7626   $84.76   $84.75   $84.80  
  Purchase #4 $199.79   3.664%   $207.1103   $207.11   $207.10   $207.10  
  Purchase #5 $116.31   13.410%   $131.9072   $131.91   $131.90   $131.90  
  Purchase #6 $40.60   4.175%   $42.2951   $42.30   $42.30   $42.30  
  Purchase #7 $216.84   5.171%   $228.0528   $228.05   $228.05   $228.10  
  7 purchase totals = $941.62       $1,022.2383   $1,022.24   $1,022.20   $1,022.30