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 $246.46   8.469%   $267.3327   $267.33   $267.35   $267.30  
  Purchase #2 $8.88   10.281%   $9.793   $9.79   $9.80   $9.80  
  Purchase #3 $48.79   6.457%   $51.9404   $51.94   $51.95   $51.90  
  Purchase #4 $17.45   10.172%   $19.225   $19.23   $19.25   $19.20  
  Purchase #5 $77.55   13.264%   $87.8362   $87.84   $87.85   $87.80  
  Purchase #6 $250.26   10.699%   $277.0353   $277.04   $277.05   $277.00  
  Purchase #7 $53.41   3.658%   $55.3637   $55.36   $55.35   $55.40  
  7 purchase totals = $702.80       $768.5263   $768.53   $768.60   $768.40