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 $92.70   11.134%   $103.0212   $103.02   $103.00   $103.00  
  Purchase #2 $97.78   10.570%   $108.1153   $108.12   $108.10   $108.10  
  Purchase #3 $178.48   4.340%   $186.226   $186.23   $186.25   $186.20  
  Purchase #4 $39.73   3.279%   $41.0327   $41.03   $41.05   $41.00  
  Purchase #5 $174.80   9.305%   $191.0651   $191.07   $191.05   $191.10  
  Purchase #6 $86.30   12.144%   $96.7803   $96.78   $96.80   $96.80  
  Purchase #7 $55.48   9.409%   $60.7001   $60.70   $60.70   $60.70  
  7 purchase totals = $725.27       $786.9407   $786.95   $786.95   $786.90