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 $194.98   10.582%   $215.6128   $215.61   $215.60   $215.60  
  Purchase #2 $56.52   3.551%   $58.527   $58.53   $58.55   $58.50  
  Purchase #3 $157.99   4.139%   $164.5292   $164.53   $164.55   $164.50  
  Purchase #4 $198.40   6.213%   $210.7266   $210.73   $210.75   $210.70  
  Purchase #5 $132.51   12.432%   $148.9836   $148.98   $149.00   $149.00  
  Purchase #6 $184.32   9.759%   $202.3078   $202.31   $202.30   $202.30  
  Purchase #7 $62.48   5.584%   $65.9689   $65.97   $65.95   $66.00  
  7 purchase totals = $987.20       $1,066.6559   $1,066.66   $1,066.70   $1,066.60