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 $33.46   7.130%   $35.8457   $35.85   $35.85   $35.80  
  Purchase #2 $58.90   4.690%   $61.6624   $61.66   $61.65   $61.70  
  Purchase #3 $14.74   7.711%   $15.8766   $15.88   $15.90   $15.90  
  Purchase #4 $201.65   4.627%   $210.9803   $210.98   $211.00   $211.00  
  Purchase #5 $34.95   7.869%   $37.7002   $37.70   $37.70   $37.70  
  Purchase #6 $80.66   6.368%   $85.7964   $85.80   $85.80   $85.80  
  Purchase #7 $180.91   11.685%   $202.0493   $202.05   $202.05   $202.00  
  7 purchase totals = $605.27       $649.9109   $649.92   $649.95   $649.90