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 $59.86   9.398%   $65.4856   $65.49   $65.50   $65.50  
  Purchase #2 $152.40   9.812%   $167.3535   $167.35   $167.35   $167.40  
  Purchase #3 $131.69   11.659%   $147.0437   $147.04   $147.05   $147.00  
  Purchase #4 $198.97   7.860%   $214.609   $214.61   $214.60   $214.60  
  Purchase #5 $93.41   9.445%   $102.2326   $102.23   $102.25   $102.20  
  Purchase #6 $169.61   6.704%   $180.9807   $180.98   $181.00   $181.00  
  Purchase #7 $94.45   4.323%   $98.5331   $98.53   $98.55   $98.50  
  7 purchase totals = $900.39       $976.2382   $976.23   $976.30   $976.20