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 $91.43   5.407%   $96.3736   $96.37   $96.35   $96.40  
  Purchase #2 $193.56   10.581%   $214.0406   $214.04   $214.05   $214.00  
  Purchase #3 $166.84   5.181%   $175.484   $175.48   $175.50   $175.50  
  Purchase #4 $57.60   8.420%   $62.4499   $62.45   $62.45   $62.40  
  Purchase #5 $184.68   5.245%   $194.3665   $194.37   $194.35   $194.40  
  Purchase #6 $48.65   4.500%   $50.8393   $50.84   $50.85   $50.80  
  Purchase #7 $28.88   7.392%   $31.0148   $31.01   $31.00   $31.00  
  7 purchase totals = $771.64       $824.5687   $824.56   $824.55   $824.50