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 $59.68   3.376%   $61.6948   $61.69   $61.70   $61.70  
  Purchase #2 $232.62   6.182%   $247.0006   $247.00   $247.00   $247.00  
  Purchase #3 $38.92   6.343%   $41.3887   $41.39   $41.40   $41.40  
  Purchase #4 $12.80   5.529%   $13.5077   $13.51   $13.50   $13.50  
  Purchase #5 $19.30   6.535%   $20.5613   $20.56   $20.55   $20.60  
  Purchase #6 $75.45   3.159%   $77.8335   $77.83   $77.85   $77.80  
  Purchase #7 $59.38   9.416%   $64.9712   $64.97   $64.95   $65.00  
  7 purchase totals = $498.15       $526.9578   $526.95   $526.95   $527.00