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 $91.26   4.113%   $95.0135   $95.01   $95.00   $95.00  
  Purchase #2 $96.89   4.735%   $101.4777   $101.48   $101.50   $101.50  
  Purchase #3 $75.39   6.261%   $80.1102   $80.11   $80.10   $80.10  
  Purchase #4 $141.43   13.690%   $160.7918   $160.79   $160.80   $160.80  
  Purchase #5 $176.75   4.241%   $184.246   $184.25   $184.25   $184.20  
  Purchase #6 $58.40   7.319%   $62.6743   $62.67   $62.65   $62.70  
  Purchase #7 $97.62   3.284%   $100.8258   $100.83   $100.85   $100.80  
  7 purchase totals = $737.74       $785.1393   $785.14   $785.15   $785.10