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 $219.69   8.195%   $237.6936   $237.69   $237.70   $237.70  
  Purchase #2 $201.52   4.587%   $210.7637   $210.76   $210.75   $210.80  
  Purchase #3 $43.79   4.712%   $45.8534   $45.85   $45.85   $45.90  
  Purchase #4 $63.86   11.495%   $71.2007   $71.20   $71.20   $71.20  
  Purchase #5 $214.32   13.835%   $243.9712   $243.97   $243.95   $244.00  
  Purchase #6 $232.89   4.586%   $243.5703   $243.57   $243.55   $243.60  
  Purchase #7 $23.54   11.847%   $26.3288   $26.33   $26.35   $26.30  
  7 purchase totals = $999.61       $1,079.3817   $1,079.37   $1,079.35   $1,079.50