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 $181.60   10.862%   $201.3254   $201.33   $201.35   $201.30  
  Purchase #2 $137.58   8.348%   $149.0652   $149.07   $149.05   $149.10  
  Purchase #3 $197.30   7.799%   $212.6874   $212.69   $212.70   $212.70  
  Purchase #4 $16.83   8.490%   $18.2589   $18.26   $18.25   $18.30  
  Purchase #5 $211.27   10.635%   $233.7386   $233.74   $233.75   $233.70  
  Purchase #6 $56.39   4.781%   $59.086   $59.09   $59.10   $59.10  
  Purchase #7 $122.25   3.160%   $126.1131   $126.11   $126.10   $126.10  
  7 purchase totals = $923.22       $1,000.2746   $1,000.29   $1,000.30   $1,000.30