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 $140.36   11.656%   $156.7204   $156.72   $156.70   $156.70  
  Purchase #2 $126.34   13.130%   $142.9284   $142.93   $142.95   $142.90  
  Purchase #3 $21.79   8.860%   $23.7206   $23.72   $23.70   $23.70  
  Purchase #4 $91.88   5.534%   $96.9646   $96.96   $96.95   $97.00  
  Purchase #5 $169.84   6.403%   $180.7149   $180.71   $180.70   $180.70  
  Purchase #6 $6.43   9.161%   $7.0191   $7.02   $7.00   $7.00  
  Purchase #7 $195.47   4.270%   $203.8166   $203.82   $203.80   $203.80  
  7 purchase totals = $752.11       $811.8846   $811.88   $811.80   $811.80