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 $141.59   6.604%   $150.9406   $150.94   $150.95   $150.90  
  Purchase #2 $150.87   11.872%   $168.7813   $168.78   $168.80   $168.80  
  Purchase #3 $244.26   10.166%   $269.0915   $269.09   $269.10   $269.10  
  Purchase #4 $181.26   7.298%   $194.4884   $194.49   $194.50   $194.50  
  Purchase #5 $213.35   13.169%   $241.4461   $241.45   $241.45   $241.40  
  Purchase #6 $64.26   10.447%   $70.9732   $70.97   $70.95   $71.00  
  Purchase #7 $55.61   8.834%   $60.5226   $60.52   $60.50   $60.50  
  7 purchase totals = $1,051.20       $1,156.2437   $1,156.24   $1,156.25   $1,156.20