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 $58.41   11.260%   $64.987   $64.99   $65.00   $65.00  
  Purchase #2 $204.55   10.766%   $226.5719   $226.57   $226.55   $226.60  
  Purchase #3 $224.41   4.220%   $233.8801   $233.88   $233.90   $233.90  
  Purchase #4 $67.30   6.814%   $71.8858   $71.89   $71.90   $71.90  
  Purchase #5 $224.79   9.542%   $246.2395   $246.24   $246.25   $246.20  
  Purchase #6 $140.68   9.658%   $154.2669   $154.27   $154.25   $154.30  
  Purchase #7 $8.27   7.503%   $8.8905   $8.89   $8.90   $8.90  
  7 purchase totals = $928.41       $1,006.7217   $1,006.73   $1,006.75   $1,006.80