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 $85.26   13.123%   $96.4487   $96.45   $96.45   $96.40  
  Purchase #2 $162.71   13.490%   $184.6596   $184.66   $184.65   $184.70  
  Purchase #3 $202.34   11.741%   $226.0967   $226.10   $226.10   $226.10  
  Purchase #4 $176.35   7.177%   $189.0066   $189.01   $189.00   $189.00  
  Purchase #5 $99.27   12.461%   $111.64   $111.64   $111.65   $111.60  
  Purchase #6 $219.48   6.361%   $233.4411   $233.44   $233.45   $233.40  
  Purchase #7 $206.71   10.852%   $229.1422   $229.14   $229.15   $229.10  
  7 purchase totals = $1,152.12       $1,270.4349   $1,270.44   $1,270.45   $1,270.30