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 $180.61   8.126%   $195.2864   $195.29   $195.30   $195.30  
  Purchase #2 $21.88   4.279%   $22.8162   $22.82   $22.80   $22.80  
  Purchase #3 $120.47   7.544%   $129.5583   $129.56   $129.55   $129.60  
  Purchase #4 $152.87   3.345%   $157.9835   $157.98   $158.00   $158.00  
  Purchase #5 $187.31   5.532%   $197.672   $197.67   $197.65   $197.70  
  Purchase #6 $11.98   8.810%   $13.0354   $13.04   $13.05   $13.00  
  Purchase #7 $64.59   4.482%   $67.4849   $67.48   $67.50   $67.50  
  7 purchase totals = $739.71       $783.8367   $783.84   $783.85   $783.90