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 $114.97   8.510%   $124.7539   $124.75   $124.75   $124.80  
  Purchase #2 $130.61   9.636%   $143.1956   $143.20   $143.20   $143.20  
  Purchase #3 $240.35   13.150%   $271.956   $271.96   $271.95   $272.00  
  Purchase #4 $219.30   4.715%   $229.64   $229.64   $229.65   $229.60  
  Purchase #5 $183.52   11.327%   $204.3073   $204.31   $204.30   $204.30  
  Purchase #6 $39.52   8.648%   $42.9377   $42.94   $42.95   $42.90  
  Purchase #7 $183.97   5.727%   $194.506   $194.51   $194.50   $194.50  
  7 purchase totals = $1,112.24       $1,211.2965   $1,211.31   $1,211.30   $1,211.30