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 $33.47   13.576%   $38.0139   $38.01   $38.00   $38.00  
  Purchase #2 $164.98   5.676%   $174.3443   $174.34   $174.35   $174.30  
  Purchase #3 $101.47   7.161%   $108.7363   $108.74   $108.75   $108.70  
  Purchase #4 $234.73   12.428%   $263.9022   $263.90   $263.90   $263.90  
  Purchase #5 $232.90   8.622%   $252.9806   $252.98   $253.00   $253.00  
  Purchase #6 $118.73   7.834%   $128.0313   $128.03   $128.05   $128.00  
  Purchase #7 $89.90   4.569%   $94.0075   $94.01   $94.00   $94.00  
  7 purchase totals = $976.18       $1,060.0161   $1,060.01   $1,060.05   $1,059.90