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 $167.31   9.682%   $183.509   $183.51   $183.50   $183.50  
  Purchase #2 $94.65   12.694%   $106.6649   $106.66   $106.65   $106.70  
  Purchase #3 $71.87   7.501%   $77.261   $77.26   $77.25   $77.30  
  Purchase #4 $149.44   12.242%   $167.7344   $167.73   $167.75   $167.70  
  Purchase #5 $141.99   9.703%   $155.7673   $155.77   $155.75   $155.80  
  Purchase #6 $236.47   10.316%   $260.8642   $260.86   $260.85   $260.90  
  Purchase #7 $135.84   9.343%   $148.5315   $148.53   $148.55   $148.50  
  7 purchase totals = $997.57       $1,100.3323   $1,100.32   $1,100.30   $1,100.40