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 $96.98   8.208%   $104.9401   $104.94   $104.95   $104.90  
  Purchase #2 $31.33   6.781%   $33.4545   $33.45   $33.45   $33.50  
  Purchase #3 $186.84   10.209%   $205.9145   $205.91   $205.90   $205.90  
  Purchase #4 $221.51   9.173%   $241.8291   $241.83   $241.85   $241.80  
  Purchase #5 $54.55   6.217%   $57.9414   $57.94   $57.95   $57.90  
  Purchase #6 $103.43   13.817%   $117.7209   $117.72   $117.70   $117.70  
  Purchase #7 $201.92   4.806%   $211.6243   $211.62   $211.60   $211.60  
  7 purchase totals = $896.56       $973.4248   $973.41   $973.40   $973.30