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 $67.86   9.264%   $74.1466   $74.15   $74.15   $74.10  
  Purchase #2 $168.65   13.590%   $191.5695   $191.57   $191.55   $191.60  
  Purchase #3 $245.68   11.679%   $274.373   $274.37   $274.35   $274.40  
  Purchase #4 $213.81   7.608%   $230.0767   $230.08   $230.10   $230.10  
  Purchase #5 $18.63   6.648%   $19.8685   $19.87   $19.85   $19.90  
  Purchase #6 $243.91   4.323%   $254.4542   $254.45   $254.45   $254.50  
  Purchase #7 $246.63   7.794%   $265.8523   $265.85   $265.85   $265.90  
  7 purchase totals = $1,205.17       $1,310.3408   $1,310.34   $1,310.30   $1,310.50