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 $231.87   8.659%   $251.9476   $251.95   $251.95   $251.90  
  Purchase #2 $12.92   10.690%   $14.3011   $14.30   $14.30   $14.30  
  Purchase #3 $111.95   7.179%   $119.9869   $119.99   $120.00   $120.00  
  Purchase #4 $110.70   8.763%   $120.4006   $120.40   $120.40   $120.40  
  Purchase #5 $187.67   8.666%   $203.9335   $203.93   $203.95   $203.90  
  Purchase #6 $154.53   9.443%   $169.1223   $169.12   $169.10   $169.10  
  Purchase #7 $165.27   5.496%   $174.3532   $174.35   $174.35   $174.40  
  7 purchase totals = $974.91       $1,054.0452   $1,054.04   $1,054.05   $1,054.00