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 $67.55   9.686%   $74.0929   $74.09   $74.10   $74.10  
  Purchase #2 $110.29   6.824%   $117.8162   $117.82   $117.80   $117.80  
  Purchase #3 $216.63   11.398%   $241.3215   $241.32   $241.30   $241.30  
  Purchase #4 $99.63   10.357%   $109.9487   $109.95   $109.95   $109.90  
  Purchase #5 $184.96   6.252%   $196.5237   $196.52   $196.50   $196.50  
  Purchase #6 $86.57   12.869%   $97.7107   $97.71   $97.70   $97.70  
  Purchase #7 $193.49   5.280%   $203.7063   $203.71   $203.70   $203.70  
  7 purchase totals = $959.12       $1,041.1200   $1,041.12   $1,041.05   $1,041.00