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 $223.95   10.748%   $248.0201   $248.02   $248.00   $248.00  
  Purchase #2 $144.52   10.600%   $159.8391   $159.84   $159.85   $159.80  
  Purchase #3 $184.64   12.616%   $207.9342   $207.93   $207.95   $207.90  
  Purchase #4 $101.31   6.385%   $107.7786   $107.78   $107.80   $107.80  
  Purchase #5 $54.70   8.650%   $59.4316   $59.43   $59.45   $59.40  
  Purchase #6 $72.50   5.368%   $76.3918   $76.39   $76.40   $76.40  
  Purchase #7 $164.30   10.640%   $181.7815   $181.78   $181.80   $181.80  
  7 purchase totals = $945.92       $1,041.1769   $1,041.17   $1,041.25   $1,041.10