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 $176.81   13.365%   $200.4407   $200.44   $200.45   $200.40  
  Purchase #2 $83.82   9.129%   $91.4719   $91.47   $91.45   $91.50  
  Purchase #3 $166.51   5.551%   $175.753   $175.75   $175.75   $175.80  
  Purchase #4 $41.50   13.277%   $47.01   $47.01   $47.00   $47.00  
  Purchase #5 $166.25   13.332%   $188.4145   $188.41   $188.40   $188.40  
  Purchase #6 $169.97   11.262%   $189.112   $189.11   $189.10   $189.10  
  Purchase #7 $194.61   5.442%   $205.2007   $205.20   $205.20   $205.20  
  7 purchase totals = $999.47       $1,097.4028   $1,097.39   $1,097.35   $1,097.40