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 $176.50   13.743%   $200.7564   $200.76   $200.75   $200.80  
  Purchase #2 $210.46   6.320%   $223.7611   $223.76   $223.75   $223.80  
  Purchase #3 $68.64   9.118%   $74.8986   $74.90   $74.90   $74.90  
  Purchase #4 $134.70   13.693%   $153.1445   $153.14   $153.15   $153.10  
  Purchase #5 $133.27   8.373%   $144.4287   $144.43   $144.45   $144.40  
  Purchase #6 $201.40   11.377%   $224.3133   $224.31   $224.30   $224.30  
  Purchase #7 $213.31   7.590%   $229.5002   $229.50   $229.50   $229.50  
  7 purchase totals = $1,138.28       $1,250.8028   $1,250.80   $1,250.80   $1,250.80