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 $245.76   9.573%   $269.2866   $269.29   $269.30   $269.30  
  Purchase #2 $14.53   10.831%   $16.1037   $16.10   $16.10   $16.10  
  Purchase #3 $219.80   9.739%   $241.2063   $241.21   $241.20   $241.20  
  Purchase #4 $20.93   8.779%   $22.7674   $22.77   $22.75   $22.80  
  Purchase #5 $83.90   5.124%   $88.199   $88.20   $88.20   $88.20  
  Purchase #6 $245.96   3.650%   $254.9375   $254.94   $254.95   $254.90  
  Purchase #7 $180.91   8.346%   $196.0087   $196.01   $196.00   $196.00  
  7 purchase totals = $1,011.79       $1,088.5092   $1,088.52   $1,088.50   $1,088.50