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 $55.99   11.363%   $62.3521   $62.35   $62.35   $62.40  
  Purchase #2 $143.89   7.273%   $154.3551   $154.36   $154.35   $154.40  
  Purchase #3 $137.60   8.577%   $149.402   $149.40   $149.40   $149.40  
  Purchase #4 $148.59   5.573%   $156.8709   $156.87   $156.85   $156.90  
  Purchase #5 $71.75   4.644%   $75.0821   $75.08   $75.10   $75.10  
  Purchase #6 $240.98   13.722%   $274.0473   $274.05   $274.05   $274.00  
  Purchase #7 $147.68   12.221%   $165.728   $165.73   $165.75   $165.70  
  7 purchase totals = $946.48       $1,037.8375   $1,037.84   $1,037.85   $1,037.90