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 $63.74   4.278%   $66.4668   $66.47   $66.45   $66.50  
  Purchase #2 $204.38   3.229%   $210.9794   $210.98   $211.00   $211.00  
  Purchase #3 $92.99   6.248%   $98.8   $98.80   $98.80   $98.80  
  Purchase #4 $225.55   5.310%   $237.5267   $237.53   $237.55   $237.50  
  Purchase #5 $234.63   13.668%   $266.6992   $266.70   $266.70   $266.70  
  Purchase #6 $242.68   5.586%   $256.2361   $256.24   $256.25   $256.20  
  Purchase #7 $52.28   7.761%   $56.3375   $56.34   $56.35   $56.30  
  7 purchase totals = $1,116.25       $1,193.0457   $1,193.06   $1,193.10   $1,193.00