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 $78.41   5.432%   $82.6692   $82.67   $82.65   $82.70  
  Purchase #2 $213.53   9.574%   $233.9734   $233.97   $233.95   $234.00  
  Purchase #3 $55.79   4.444%   $58.2693   $58.27   $58.25   $58.30  
  Purchase #4 $200.58   9.343%   $219.3202   $219.32   $219.30   $219.30  
  Purchase #5 $229.48   13.571%   $260.6227   $260.62   $260.60   $260.60  
  Purchase #6 $185.96   9.444%   $203.5221   $203.52   $203.50   $203.50  
  Purchase #7 $94.51   12.555%   $106.3757   $106.38   $106.40   $106.40  
  7 purchase totals = $1,058.26       $1,164.7526   $1,164.75   $1,164.65   $1,164.80