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 $202.68   10.180%   $223.3128   $223.31   $223.30   $223.30  
  Purchase #2 $34.67   9.395%   $37.9272   $37.93   $37.95   $37.90  
  Purchase #3 $19.44   10.739%   $21.5277   $21.53   $21.55   $21.50  
  Purchase #4 $160.76   7.578%   $172.9424   $172.94   $172.95   $172.90  
  Purchase #5 $87.48   11.428%   $97.4772   $97.48   $97.50   $97.50  
  Purchase #6 $235.85   3.253%   $243.5222   $243.52   $243.50   $243.50  
  Purchase #7 $233.32   10.230%   $257.1886   $257.19   $257.20   $257.20  
  7 purchase totals = $974.20       $1,053.8981   $1,053.90   $1,053.95   $1,053.80