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 $105.96   12.597%   $119.3078   $119.31   $119.30   $119.30  
  Purchase #2 $203.46   6.325%   $216.3288   $216.33   $216.35   $216.30  
  Purchase #3 $89.85   3.647%   $93.1268   $93.13   $93.15   $93.10  
  Purchase #4 $60.97   6.795%   $65.1129   $65.11   $65.10   $65.10  
  Purchase #5 $140.44   8.428%   $152.2763   $152.28   $152.30   $152.30  
  Purchase #6 $120.46   5.869%   $127.5298   $127.53   $127.55   $127.50  
  Purchase #7 $206.63   12.448%   $232.3513   $232.35   $232.35   $232.40  
  7 purchase totals = $927.77       $1,006.0337   $1,006.04   $1,006.10   $1,006.00