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 $169.61   8.310%   $183.7046   $183.70   $183.70   $183.70  
  Purchase #2 $45.60   8.759%   $49.5941   $49.59   $49.60   $49.60  
  Purchase #3 $112.87   6.784%   $120.5271   $120.53   $120.55   $120.50  
  Purchase #4 $98.26   7.530%   $105.659   $105.66   $105.65   $105.70  
  Purchase #5 $105.74   10.288%   $116.6185   $116.62   $116.60   $116.60  
  Purchase #6 $146.31   10.306%   $161.3887   $161.39   $161.40   $161.40  
  Purchase #7 $27.39   7.852%   $29.5407   $29.54   $29.55   $29.50  
  7 purchase totals = $705.78       $767.0327   $767.03   $767.05   $767.00