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 $234.88   12.721%   $264.7591   $264.76   $264.75   $264.80  
  Purchase #2 $160.97   9.278%   $175.9048   $175.90   $175.90   $175.90  
  Purchase #3 $57.97   10.134%   $63.8447   $63.84   $63.85   $63.80  
  Purchase #4 $115.98   9.676%   $127.2022   $127.20   $127.20   $127.20  
  Purchase #5 $106.44   13.225%   $120.5167   $120.52   $120.50   $120.50  
  Purchase #6 $170.29   12.128%   $190.9428   $190.94   $190.95   $190.90  
  Purchase #7 $145.76   10.702%   $161.3592   $161.36   $161.35   $161.40  
  7 purchase totals = $992.29       $1,104.5295   $1,104.52   $1,104.50   $1,104.50