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 $192.88   6.336%   $205.1009   $205.10   $205.10   $205.10  
  Purchase #2 $90.96   5.522%   $95.9828   $95.98   $96.00   $96.00  
  Purchase #3 $53.52   4.249%   $55.7941   $55.79   $55.80   $55.80  
  Purchase #4 $118.60   7.507%   $127.5033   $127.50   $127.50   $127.50  
  Purchase #5 $191.52   8.508%   $207.8145   $207.81   $207.80   $207.80  
  Purchase #6 $202.99   8.527%   $220.299   $220.30   $220.30   $220.30  
  Purchase #7 $41.79   8.355%   $45.2816   $45.28   $45.30   $45.30  
  7 purchase totals = $892.26       $957.7762   $957.76   $957.80   $957.80