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 $203.31   4.478%   $212.4142   $212.41   $212.40   $212.40  
  Purchase #2 $211.47   6.391%   $224.985   $224.99   $225.00   $225.00  
  Purchase #3 $84.77   13.214%   $95.9715   $95.97   $95.95   $96.00  
  Purchase #4 $194.47   10.335%   $214.5685   $214.57   $214.55   $214.60  
  Purchase #5 $31.96   10.437%   $35.2957   $35.30   $35.30   $35.30  
  Purchase #6 $170.89   9.429%   $187.0032   $187.00   $187.00   $187.00  
  Purchase #7 $94.41   12.272%   $105.996   $106.00   $106.00   $106.00  
  7 purchase totals = $991.28       $1,076.2341   $1,076.24   $1,076.20   $1,076.30