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 $68.62   9.433%   $75.0929   $75.09   $75.10   $75.10  
  Purchase #2 $186.94   12.849%   $210.9599   $210.96   $210.95   $211.00  
  Purchase #3 $19.44   11.442%   $21.6643   $21.66   $21.65   $21.70  
  Purchase #4 $225.87   13.760%   $256.9497   $256.95   $256.95   $256.90  
  Purchase #5 $52.85   9.851%   $58.0563   $58.06   $58.05   $58.10  
  Purchase #6 $41.49   10.788%   $45.9659   $45.97   $45.95   $46.00  
  Purchase #7 $80.54   6.698%   $85.9346   $85.93   $85.95   $85.90  
  7 purchase totals = $675.75       $754.6236   $754.62   $754.60   $754.70