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 $83.31   12.641%   $93.8412   $93.84   $93.85   $93.80  
  Purchase #2 $152.83   5.322%   $160.9636   $160.96   $160.95   $161.00  
  Purchase #3 $131.31   10.843%   $145.5479   $145.55   $145.55   $145.50  
  Purchase #4 $92.38   3.151%   $95.2909   $95.29   $95.30   $95.30  
  Purchase #5 $119.40   8.349%   $129.3687   $129.37   $129.35   $129.40  
  Purchase #6 $246.94   10.847%   $273.7256   $273.73   $273.75   $273.70  
  Purchase #7 $153.27   6.744%   $163.6065   $163.61   $163.60   $163.60  
  7 purchase totals = $979.44       $1,062.3444   $1,062.35   $1,062.35   $1,062.30