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 $87.68   6.440%   $93.3266   $93.33   $93.35   $93.30  
  Purchase #2 $225.59   7.252%   $241.9498   $241.95   $241.95   $241.90  
  Purchase #3 $37.61   5.373%   $39.6308   $39.63   $39.65   $39.60  
  Purchase #4 $158.72   4.656%   $166.11   $166.11   $166.10   $166.10  
  Purchase #5 $19.60   4.740%   $20.529   $20.53   $20.55   $20.50  
  Purchase #6 $99.36   4.200%   $103.5331   $103.53   $103.55   $103.50  
  Purchase #7 $245.66   6.651%   $261.9988   $262.00   $262.00   $262.00  
  7 purchase totals = $874.22       $927.0781   $927.08   $927.15   $926.90