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 $94.58   5.170%   $99.4698   $99.47   $99.45   $99.50  
  Purchase #2 $164.72   4.241%   $171.7058   $171.71   $171.70   $171.70  
  Purchase #3 $184.45   9.469%   $201.9156   $201.92   $201.90   $201.90  
  Purchase #4 $206.28   6.317%   $219.3107   $219.31   $219.30   $219.30  
  Purchase #5 $124.52   7.504%   $133.864   $133.86   $133.85   $133.90  
  Purchase #6 $119.73   5.526%   $126.3463   $126.35   $126.35   $126.30  
  Purchase #7 $82.49   10.324%   $91.0063   $91.01   $91.00   $91.00  
  7 purchase totals = $976.77       $1,043.6185   $1,043.63   $1,043.55   $1,043.60