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 $167.96   4.206%   $175.0244   $175.02   $175.00   $175.00  
  Purchase #2 $60.31   6.203%   $64.051   $64.05   $64.05   $64.10  
  Purchase #3 $181.99   13.626%   $206.788   $206.79   $206.80   $206.80  
  Purchase #4 $58.36   10.624%   $64.5602   $64.56   $64.55   $64.60  
  Purchase #5 $101.66   7.456%   $109.2398   $109.24   $109.25   $109.20  
  Purchase #6 $200.45   11.567%   $223.6361   $223.64   $223.65   $223.60  
  Purchase #7 $172.78   10.645%   $191.1724   $191.17   $191.15   $191.20  
  7 purchase totals = $943.51       $1,034.4719   $1,034.47   $1,034.45   $1,034.50