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 $16.27   8.597%   $17.6687   $17.67   $17.65   $17.70  
  Purchase #2 $134.25   10.362%   $148.161   $148.16   $148.15   $148.20  
  Purchase #3 $229.26   9.170%   $250.2831   $250.28   $250.30   $250.30  
  Purchase #4 $158.86   3.294%   $164.0928   $164.09   $164.10   $164.10  
  Purchase #5 $159.70   11.576%   $178.1869   $178.19   $178.20   $178.20  
  Purchase #6 $172.60   4.431%   $180.2479   $180.25   $180.25   $180.20  
  Purchase #7 $219.88   12.515%   $247.398   $247.40   $247.40   $247.40  
  7 purchase totals = $1,090.82       $1,186.0384   $1,186.04   $1,186.05   $1,186.10