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 $111.26   11.173%   $123.6911   $123.69   $123.70   $123.70  
  Purchase #2 $111.69   5.631%   $117.9793   $117.98   $118.00   $118.00  
  Purchase #3 $96.88   8.668%   $105.2776   $105.28   $105.30   $105.30  
  Purchase #4 $154.37   4.558%   $161.4062   $161.41   $161.40   $161.40  
  Purchase #5 $126.67   7.815%   $136.5693   $136.57   $136.55   $136.60  
  Purchase #6 $219.59   10.735%   $243.163   $243.16   $243.15   $243.20  
  Purchase #7 $241.52   11.462%   $269.203   $269.20   $269.20   $269.20  
  7 purchase totals = $1,061.98       $1,157.2895   $1,157.29   $1,157.30   $1,157.40