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 $52.63   9.836%   $57.8067   $57.81   $57.80   $57.80  
  Purchase #2 $113.26   4.688%   $118.5696   $118.57   $118.55   $118.60  
  Purchase #3 $189.67   11.239%   $210.987   $210.99   $211.00   $211.00  
  Purchase #4 $202.73   10.406%   $223.8261   $223.83   $223.85   $223.80  
  Purchase #5 $230.65   11.216%   $256.5197   $256.52   $256.50   $256.50  
  Purchase #6 $62.70   7.322%   $67.2909   $67.29   $67.30   $67.30  
  Purchase #7 $91.47   7.692%   $98.5059   $98.51   $98.50   $98.50  
  7 purchase totals = $943.11       $1,033.5059   $1,033.52   $1,033.50   $1,033.50