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 $58.72   13.647%   $66.7335   $66.73   $66.75   $66.70  
  Purchase #2 $202.38   4.113%   $210.7039   $210.70   $210.70   $210.70  
  Purchase #3 $196.97   12.504%   $221.5991   $221.60   $221.60   $221.60  
  Purchase #4 $32.64   9.185%   $35.638   $35.64   $35.65   $35.60  
  Purchase #5 $80.55   4.205%   $83.9371   $83.94   $83.95   $83.90  
  Purchase #6 $239.31   6.207%   $254.164   $254.16   $254.15   $254.20  
  Purchase #7 $169.81   13.560%   $192.8362   $192.84   $192.85   $192.80  
  7 purchase totals = $980.38       $1,065.6118   $1,065.61   $1,065.65   $1,065.50