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 $204.79   10.674%   $226.6493   $226.65   $226.65   $226.60  
  Purchase #2 $94.47   7.370%   $101.4324   $101.43   $101.45   $101.40  
  Purchase #3 $16.36   3.762%   $16.9755   $16.98   $17.00   $17.00  
  Purchase #4 $9.81   6.436%   $10.4414   $10.44   $10.45   $10.40  
  Purchase #5 $167.46   5.304%   $176.3421   $176.34   $176.35   $176.30  
  Purchase #6 $56.28   4.245%   $58.6691   $58.67   $58.65   $58.70  
  Purchase #7 $107.52   12.120%   $120.5514   $120.55   $120.55   $120.60  
  7 purchase totals = $656.69       $711.0612   $711.06   $711.10   $711.00