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 $238.54   10.635%   $263.9087   $263.91   $263.90   $263.90  
  Purchase #2 $174.99   5.263%   $184.1997   $184.20   $184.20   $184.20  
  Purchase #3 $120.55   5.111%   $126.7113   $126.71   $126.70   $126.70  
  Purchase #4 $189.69   8.770%   $206.3258   $206.33   $206.35   $206.30  
  Purchase #5 $219.27   11.317%   $244.0848   $244.08   $244.10   $244.10  
  Purchase #6 $234.35   6.663%   $249.9647   $249.96   $249.95   $250.00  
  Purchase #7 $26.45   7.218%   $28.3592   $28.36   $28.35   $28.40  
  7 purchase totals = $1,203.84       $1,303.5542   $1,303.55   $1,303.55   $1,303.60