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 $86.53   9.394%   $94.6586   $94.66   $94.65   $94.70  
  Purchase #2 $172.93   11.287%   $192.4486   $192.45   $192.45   $192.40  
  Purchase #3 $235.57   9.485%   $257.9138   $257.91   $257.90   $257.90  
  Purchase #4 $46.61   10.124%   $51.3288   $51.33   $51.35   $51.30  
  Purchase #5 $173.25   11.365%   $192.9399   $192.94   $192.95   $192.90  
  Purchase #6 $153.87   4.130%   $160.2248   $160.22   $160.20   $160.20  
  Purchase #7 $169.52   11.301%   $188.6775   $188.68   $188.70   $188.70  
  7 purchase totals = $1,038.28       $1,138.1920   $1,138.19   $1,138.20   $1,138.10