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 $68.76   6.572%   $73.2789   $73.28   $73.30   $73.30  
  Purchase #2 $192.84   4.421%   $201.3655   $201.37   $201.35   $201.40  
  Purchase #3 $176.97   9.337%   $193.4937   $193.49   $193.50   $193.50  
  Purchase #4 $246.46   4.220%   $256.8606   $256.86   $256.85   $256.90  
  Purchase #5 $113.52   9.565%   $124.3782   $124.38   $124.40   $124.40  
  Purchase #6 $27.94   12.370%   $31.3962   $31.40   $31.40   $31.40  
  Purchase #7 $181.81   13.287%   $205.9671   $205.97   $205.95   $206.00  
  7 purchase totals = $1,008.30       $1,086.7402   $1,086.75   $1,086.75   $1,086.90