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 $244.93   7.688%   $263.7602   $263.76   $263.75   $263.80  
  Purchase #2 $154.59   13.415%   $175.3282   $175.33   $175.35   $175.30  
  Purchase #3 $153.31   7.339%   $164.5614   $164.56   $164.55   $164.60  
  Purchase #4 $54.62   8.375%   $59.1944   $59.19   $59.20   $59.20  
  Purchase #5 $54.42   3.677%   $56.421   $56.42   $56.40   $56.40  
  Purchase #6 $247.40   8.716%   $268.9634   $268.96   $268.95   $269.00  
  Purchase #7 $26.73   7.743%   $28.7997   $28.80   $28.80   $28.80  
  7 purchase totals = $936.00       $1,017.0283   $1,017.02   $1,017.00   $1,017.10