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 $204.62   4.349%   $213.5189   $213.52   $213.50   $213.50  
  Purchase #2 $244.46   11.512%   $272.6022   $272.60   $272.60   $272.60  
  Purchase #3 $32.77   7.232%   $35.1399   $35.14   $35.15   $35.10  
  Purchase #4 $135.29   6.210%   $143.6915   $143.69   $143.70   $143.70  
  Purchase #5 $205.68   3.144%   $212.1466   $212.15   $212.15   $212.10  
  Purchase #6 $145.33   10.578%   $160.703   $160.70   $160.70   $160.70  
  Purchase #7 $156.44   10.759%   $173.2714   $173.27   $173.25   $173.30  
  7 purchase totals = $1,124.59       $1,211.0735   $1,211.07   $1,211.05   $1,211.00