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 $204.70   13.812%   $232.9732   $232.97   $232.95   $233.00  
  Purchase #2 $134.39   8.313%   $145.5618   $145.56   $145.55   $145.60  
  Purchase #3 $174.54   7.541%   $187.7021   $187.70   $187.70   $187.70  
  Purchase #4 $74.87   13.553%   $85.0171   $85.02   $85.00   $85.00  
  Purchase #5 $65.86   9.261%   $71.9593   $71.96   $71.95   $72.00  
  Purchase #6 $213.47   3.581%   $221.1144   $221.11   $221.10   $221.10  
  Purchase #7 $68.65   6.458%   $73.0834   $73.08   $73.10   $73.10  
  7 purchase totals = $936.48       $1,017.4113   $1,017.40   $1,017.35   $1,017.50