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 $145.63   9.334%   $159.2231   $159.22   $159.20   $159.20  
  Purchase #2 $209.73   7.564%   $225.594   $225.59   $225.60   $225.60  
  Purchase #3 $191.83   5.309%   $202.0143   $202.01   $202.00   $202.00  
  Purchase #4 $245.52   9.548%   $268.9622   $268.96   $268.95   $269.00  
  Purchase #5 $50.36   5.851%   $53.3066   $53.31   $53.30   $53.30  
  Purchase #6 $161.90   12.638%   $182.3609   $182.36   $182.35   $182.40  
  Purchase #7 $101.84   9.595%   $111.6115   $111.61   $111.60   $111.60  
  7 purchase totals = $1,106.81       $1,203.0726   $1,203.06   $1,203.00   $1,203.10