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 $65.98   4.611%   $69.0223   $69.02   $69.00   $69.00  
  Purchase #2 $94.82   9.496%   $103.8241   $103.82   $103.80   $103.80  
  Purchase #3 $106.66   10.478%   $117.8358   $117.84   $117.85   $117.80  
  Purchase #4 $48.44   12.855%   $54.667   $54.67   $54.65   $54.70  
  Purchase #5 $187.40   8.174%   $202.7181   $202.72   $202.70   $202.70  
  Purchase #6 $152.33   7.253%   $163.3785   $163.38   $163.40   $163.40  
  Purchase #7 $37.57   7.183%   $40.2687   $40.27   $40.25   $40.30  
  7 purchase totals = $693.20       $751.7145   $751.72   $751.65   $751.70