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 $181.28   11.297%   $201.7592   $201.76   $201.75   $201.80  
  Purchase #2 $220.90   13.227%   $250.1184   $250.12   $250.10   $250.10  
  Purchase #3 $207.85   12.772%   $234.3966   $234.40   $234.40   $234.40  
  Purchase #4 $33.68   7.562%   $36.2269   $36.23   $36.25   $36.20  
  Purchase #5 $140.47   10.855%   $155.718   $155.72   $155.70   $155.70  
  Purchase #6 $98.37   11.150%   $109.3383   $109.34   $109.35   $109.30  
  Purchase #7 $102.64   10.218%   $113.1278   $113.13   $113.15   $113.10  
  7 purchase totals = $985.19       $1,100.6852   $1,100.70   $1,100.70   $1,100.60