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 $173.26   10.418%   $191.3102   $191.31   $191.30   $191.30  
  Purchase #2 $224.39   9.580%   $245.8866   $245.89   $245.90   $245.90  
  Purchase #3 $248.73   10.325%   $274.4114   $274.41   $274.40   $274.40  
  Purchase #4 $127.33   4.592%   $133.177   $133.18   $133.20   $133.20  
  Purchase #5 $226.84   12.251%   $254.6302   $254.63   $254.65   $254.60  
  Purchase #6 $80.72   9.537%   $88.4183   $88.42   $88.40   $88.40  
  Purchase #7 $137.98   8.361%   $149.5165   $149.52   $149.50   $149.50  
  7 purchase totals = $1,219.25       $1,337.3502   $1,337.36   $1,337.35   $1,337.30