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 $91.34   5.692%   $96.5391   $96.54   $96.55   $96.50  
  Purchase #2 $34.60   5.582%   $36.5314   $36.53   $36.55   $36.50  
  Purchase #3 $100.57   9.691%   $110.3162   $110.32   $110.30   $110.30  
  Purchase #4 $144.97   13.531%   $164.5859   $164.59   $164.60   $164.60  
  Purchase #5 $67.27   9.525%   $73.6775   $73.68   $73.70   $73.70  
  Purchase #6 $75.59   12.447%   $84.9987   $85.00   $85.00   $85.00  
  Purchase #7 $181.33   6.596%   $193.2905   $193.29   $193.30   $193.30  
  7 purchase totals = $695.67       $759.9393   $759.95   $760.00   $759.90