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 $218.29   11.631%   $243.6793   $243.68   $243.70   $243.70  
  Purchase #2 $61.34   12.117%   $68.7726   $68.77   $68.75   $68.80  
  Purchase #3 $25.75   3.346%   $26.6116   $26.61   $26.60   $26.60  
  Purchase #4 $150.88   7.320%   $161.9244   $161.92   $161.90   $161.90  
  Purchase #5 $206.36   3.608%   $213.8055   $213.81   $213.80   $213.80  
  Purchase #6 $210.54   8.773%   $229.0107   $229.01   $229.00   $229.00  
  Purchase #7 $102.96   3.309%   $106.3669   $106.37   $106.35   $106.40  
  7 purchase totals = $976.12       $1,050.1710   $1,050.17   $1,050.10   $1,050.20