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 $201.90   6.643%   $215.3122   $215.31   $215.30   $215.30  
  Purchase #2 $189.70   11.872%   $212.2212   $212.22   $212.20   $212.20  
  Purchase #3 $34.74   12.417%   $39.0537   $39.05   $39.05   $39.10  
  Purchase #4 $49.92   6.321%   $53.0754   $53.08   $53.10   $53.10  
  Purchase #5 $52.37   5.868%   $55.4431   $55.44   $55.45   $55.40  
  Purchase #6 $54.52   6.815%   $58.2355   $58.24   $58.25   $58.20  
  Purchase #7 $94.79   7.241%   $101.6537   $101.65   $101.65   $101.70  
  7 purchase totals = $677.94       $734.9948   $734.99   $735.00   $735.00