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 $135.57   12.302%   $152.2478   $152.25   $152.25   $152.20  
  Purchase #2 $241.25   9.528%   $264.2363   $264.24   $264.25   $264.20  
  Purchase #3 $150.57   11.107%   $167.2938   $167.29   $167.30   $167.30  
  Purchase #4 $11.62   5.170%   $12.2208   $12.22   $12.20   $12.20  
  Purchase #5 $107.87   9.373%   $117.9807   $117.98   $118.00   $118.00  
  Purchase #6 $133.64   7.649%   $143.8621   $143.86   $143.85   $143.90  
  Purchase #7 $170.70   11.871%   $190.9638   $190.96   $190.95   $191.00  
  7 purchase totals = $951.22       $1,048.8053   $1,048.80   $1,048.80   $1,048.80