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 $60.69   10.310%   $66.9471   $66.95   $66.95   $66.90  
  Purchase #2 $67.57   7.259%   $72.4749   $72.47   $72.45   $72.50  
  Purchase #3 $53.80   12.573%   $60.5643   $60.56   $60.55   $60.60  
  Purchase #4 $204.90   12.673%   $230.867   $230.87   $230.85   $230.90  
  Purchase #5 $181.69   11.786%   $203.104   $203.10   $203.10   $203.10  
  Purchase #6 $159.58   13.612%   $181.302   $181.30   $181.30   $181.30  
  Purchase #7 $29.63   5.810%   $31.3515   $31.35   $31.35   $31.40  
  7 purchase totals = $757.86       $846.6108   $846.60   $846.55   $846.70