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 $194.84   3.353%   $201.373   $201.37   $201.35   $201.40  
  Purchase #2 $127.92   11.766%   $142.9711   $142.97   $142.95   $143.00  
  Purchase #3 $90.28   9.695%   $99.0326   $99.03   $99.05   $99.00  
  Purchase #4 $129.99   3.647%   $134.7307   $134.73   $134.75   $134.70  
  Purchase #5 $198.93   9.431%   $217.6911   $217.69   $217.70   $217.70  
  Purchase #6 $225.57   9.376%   $246.7194   $246.72   $246.70   $246.70  
  Purchase #7 $32.39   7.181%   $34.7159   $34.72   $34.70   $34.70  
  7 purchase totals = $999.92       $1,077.2338   $1,077.23   $1,077.20   $1,077.20