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 $10.26   6.680%   $10.9454   $10.95   $10.95   $10.90  
  Purchase #2 $220.55   7.663%   $237.4507   $237.45   $237.45   $237.50  
  Purchase #3 $108.35   7.208%   $116.1599   $116.16   $116.15   $116.20  
  Purchase #4 $233.29   8.781%   $253.7752   $253.78   $253.80   $253.80  
  Purchase #5 $246.71   10.789%   $273.3275   $273.33   $273.35   $273.30  
  Purchase #6 $58.51   12.572%   $65.8659   $65.87   $65.85   $65.90  
  Purchase #7 $97.66   3.201%   $100.7861   $100.79   $100.80   $100.80  
  7 purchase totals = $975.33       $1,058.3107   $1,058.33   $1,058.35   $1,058.40