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 $59.39   6.796%   $63.4261   $63.43   $63.45   $63.40  
  Purchase #2 $31.44   8.315%   $34.0542   $34.05   $34.05   $34.10  
  Purchase #3 $15.29   11.531%   $17.0531   $17.05   $17.05   $17.10  
  Purchase #4 $24.31   8.297%   $26.327   $26.33   $26.35   $26.30  
  Purchase #5 $92.39   7.379%   $99.2075   $99.21   $99.20   $99.20  
  Purchase #6 $210.26   5.409%   $221.633   $221.63   $221.65   $221.60  
  Purchase #7 $145.47   4.671%   $152.2649   $152.26   $152.25   $152.30  
  7 purchase totals = $578.55       $613.9658   $613.96   $614.00   $614.00