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 $144.75   5.199%   $152.2756   $152.28   $152.30   $152.30  
  Purchase #2 $62.58   6.742%   $66.7991   $66.80   $66.80   $66.80  
  Purchase #3 $53.48   11.433%   $59.5944   $59.59   $59.60   $59.60  
  Purchase #4 $59.98   8.291%   $64.9529   $64.95   $64.95   $65.00  
  Purchase #5 $218.93   5.250%   $230.4238   $230.42   $230.40   $230.40  
  Purchase #6 $132.77   12.619%   $149.5242   $149.52   $149.50   $149.50  
  Purchase #7 $174.75   10.294%   $192.7388   $192.74   $192.75   $192.70  
  7 purchase totals = $847.24       $916.3088   $916.30   $916.30   $916.30