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 $138.28   7.490%   $148.6372   $148.64   $148.65   $148.60  
  Purchase #2 $158.65   3.460%   $164.1393   $164.14   $164.15   $164.10  
  Purchase #3 $107.90   4.752%   $113.0274   $113.03   $113.05   $113.00  
  Purchase #4 $205.50   7.148%   $220.1891   $220.19   $220.20   $220.20  
  Purchase #5 $206.31   8.530%   $223.9082   $223.91   $223.90   $223.90  
  Purchase #6 $201.68   9.297%   $220.4302   $220.43   $220.45   $220.40  
  Purchase #7 $19.45   6.712%   $20.7555   $20.76   $20.75   $20.80  
  7 purchase totals = $1,037.77       $1,111.0869   $1,111.10   $1,111.15   $1,111.00