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 $80.46   3.499%   $83.2753   $83.28   $83.30   $83.30  
  Purchase #2 $219.43   5.573%   $231.6588   $231.66   $231.65   $231.70  
  Purchase #3 $131.95   13.709%   $150.039   $150.04   $150.05   $150.00  
  Purchase #4 $178.46   12.823%   $201.3439   $201.34   $201.35   $201.30  
  Purchase #5 $242.61   8.270%   $262.6738   $262.67   $262.65   $262.70  
  Purchase #6 $152.52   13.611%   $173.2795   $173.28   $173.30   $173.30  
  Purchase #7 $165.89   5.109%   $174.3653   $174.37   $174.35   $174.40  
  7 purchase totals = $1,171.32       $1,276.6356   $1,276.64   $1,276.65   $1,276.70