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 $63.54   4.704%   $66.5289   $66.53   $66.55   $66.50  
  Purchase #2 $96.92   11.458%   $108.0251   $108.03   $108.05   $108.00  
  Purchase #3 $143.79   3.626%   $149.0038   $149.00   $149.00   $149.00  
  Purchase #4 $72.49   6.426%   $77.1482   $77.15   $77.15   $77.10  
  Purchase #5 $235.78   3.627%   $244.3317   $244.33   $244.35   $244.30  
  Purchase #6 $223.45   4.411%   $233.3064   $233.31   $233.30   $233.30  
  Purchase #7 $93.89   3.290%   $96.979   $96.98   $97.00   $97.00  
  7 purchase totals = $929.86       $975.3231   $975.33   $975.40   $975.20