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 $91.35   5.386%   $96.2701   $96.27   $96.25   $96.30  
  Purchase #2 $207.55   12.637%   $233.7781   $233.78   $233.80   $233.80  
  Purchase #3 $245.37   12.297%   $275.5431   $275.54   $275.55   $275.50  
  Purchase #4 $70.73   12.682%   $79.7   $79.70   $79.70   $79.70  
  Purchase #5 $201.43   10.785%   $223.1542   $223.15   $223.15   $223.20  
  Purchase #6 $212.52   12.432%   $238.9405   $238.94   $238.95   $238.90  
  Purchase #7 $124.75   7.688%   $134.3408   $134.34   $134.35   $134.30  
  7 purchase totals = $1,153.70       $1,281.7268   $1,281.72   $1,281.75   $1,281.70