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 $88.82   5.471%   $93.6793   $93.68   $93.70   $93.70  
  Purchase #2 $214.91   12.531%   $241.8404   $241.84   $241.85   $241.80  
  Purchase #3 $52.48   5.112%   $55.1628   $55.16   $55.15   $55.20  
  Purchase #4 $187.96   5.435%   $198.1756   $198.18   $198.20   $198.20  
  Purchase #5 $193.80   8.606%   $210.4784   $210.48   $210.50   $210.50  
  Purchase #6 $12.88   13.537%   $14.6236   $14.62   $14.60   $14.60  
  Purchase #7 $42.65   5.454%   $44.9761   $44.98   $45.00   $45.00  
  7 purchase totals = $793.50       $858.9362   $858.94   $859.00   $859.00