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 $63.35   11.374%   $70.5554   $70.56   $70.55   $70.60  
  Purchase #2 $202.73   3.138%   $209.0917   $209.09   $209.10   $209.10  
  Purchase #3 $187.74   10.106%   $206.713   $206.71   $206.70   $206.70  
  Purchase #4 $27.79   7.755%   $29.9451   $29.95   $29.95   $29.90  
  Purchase #5 $209.44   9.566%   $229.475   $229.48   $229.50   $229.50  
  Purchase #6 $193.46   13.547%   $219.668   $219.67   $219.65   $219.70  
  Purchase #7 $126.99   12.381%   $142.7126   $142.71   $142.70   $142.70  
  7 purchase totals = $1,011.50       $1,108.1608   $1,108.17   $1,108.15   $1,108.20