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 $66.82   11.754%   $74.674   $74.67   $74.65   $74.70  
  Purchase #2 $130.98   5.597%   $138.311   $138.31   $138.30   $138.30  
  Purchase #3 $172.44   8.697%   $187.4371   $187.44   $187.45   $187.40  
  Purchase #4 $124.51   4.387%   $129.9723   $129.97   $129.95   $130.00  
  Purchase #5 $106.70   10.684%   $118.0998   $118.10   $118.10   $118.10  
  Purchase #6 $240.77   6.576%   $256.603   $256.60   $256.60   $256.60  
  Purchase #7 $23.27   6.553%   $24.7949   $24.79   $24.80   $24.80  
  7 purchase totals = $865.49       $929.8921   $929.88   $929.85   $929.90