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 $66.82   7.348%   $71.7299   $71.73   $71.75   $71.70  
  Purchase #2 $106.99   11.152%   $118.9215   $118.92   $118.90   $118.90  
  Purchase #3 $247.63   12.402%   $278.3411   $278.34   $278.35   $278.30  
  Purchase #4 $191.47   5.541%   $202.0794   $202.08   $202.10   $202.10  
  Purchase #5 $37.25   6.855%   $39.8035   $39.80   $39.80   $39.80  
  Purchase #6 $71.60   4.850%   $75.0726   $75.07   $75.05   $75.10  
  Purchase #7 $245.88   9.759%   $269.8754   $269.88   $269.90   $269.90  
  7 purchase totals = $967.64       $1,055.8234   $1,055.82   $1,055.85   $1,055.80