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 $11.55   6.534%   $12.3047   $12.30   $12.30   $12.30  
  Purchase #2 $184.74   10.723%   $204.5497   $204.55   $204.55   $204.50  
  Purchase #3 $212.79   13.700%   $241.9422   $241.94   $241.95   $241.90  
  Purchase #4 $20.52   8.185%   $22.1996   $22.20   $22.20   $22.20  
  Purchase #5 $209.35   5.539%   $220.9459   $220.95   $220.95   $220.90  
  Purchase #6 $195.95   8.540%   $212.6841   $212.68   $212.70   $212.70  
  Purchase #7 $142.55   3.290%   $147.2399   $147.24   $147.25   $147.20  
  7 purchase totals = $977.45       $1,061.8661   $1,061.86   $1,061.90   $1,061.70