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 $65.47   6.261%   $69.5691   $69.57   $69.55   $69.60  
  Purchase #2 $244.59   11.383%   $272.4317   $272.43   $272.45   $272.40  
  Purchase #3 $109.63   12.104%   $122.8996   $122.90   $122.90   $122.90  
  Purchase #4 $70.76   13.533%   $80.336   $80.34   $80.35   $80.30  
  Purchase #5 $204.33   8.625%   $221.9535   $221.95   $221.95   $222.00  
  Purchase #6 $59.94   12.303%   $67.3144   $67.31   $67.30   $67.30  
  Purchase #7 $234.27   7.784%   $252.5056   $252.51   $252.50   $252.50  
  7 purchase totals = $988.99       $1,087.0099   $1,087.01   $1,087.00   $1,087.00