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 $96.76   4.354%   $100.9729   $100.97   $100.95   $101.00  
  Purchase #2 $219.66   9.451%   $240.4201   $240.42   $240.40   $240.40  
  Purchase #3 $97.72   9.146%   $106.6575   $106.66   $106.65   $106.70  
  Purchase #4 $220.36   8.195%   $238.4185   $238.42   $238.40   $238.40  
  Purchase #5 $52.57   11.506%   $58.6187   $58.62   $58.60   $58.60  
  Purchase #6 $120.29   3.325%   $124.2896   $124.29   $124.30   $124.30  
  Purchase #7 $150.69   10.288%   $166.193   $166.19   $166.20   $166.20  
  7 purchase totals = $958.05       $1,035.5703   $1,035.57   $1,035.50   $1,035.60