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 $59.32   13.544%   $67.3543   $67.35   $67.35   $67.40  
  Purchase #2 $80.33   9.436%   $87.9099   $87.91   $87.90   $87.90  
  Purchase #3 $101.79   13.747%   $115.7831   $115.78   $115.80   $115.80  
  Purchase #4 $99.29   10.416%   $109.632   $109.63   $109.65   $109.60  
  Purchase #5 $219.84   10.339%   $242.5693   $242.57   $242.55   $242.60  
  Purchase #6 $110.46   12.779%   $124.5757   $124.58   $124.60   $124.60  
  Purchase #7 $81.27   8.231%   $87.9593   $87.96   $87.95   $88.00  
  7 purchase totals = $752.30       $835.7836   $835.78   $835.80   $835.90