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 $223.97   3.601%   $232.0352   $232.04   $232.05   $232.00  
  Purchase #2 $234.93   3.124%   $242.2692   $242.27   $242.25   $242.30  
  Purchase #3 $35.79   11.450%   $39.888   $39.89   $39.90   $39.90  
  Purchase #4 $227.52   6.492%   $242.2906   $242.29   $242.30   $242.30  
  Purchase #5 $216.80   7.411%   $232.867   $232.87   $232.85   $232.90  
  Purchase #6 $205.66   7.833%   $221.7693   $221.77   $221.75   $221.80  
  Purchase #7 $120.29   11.615%   $134.2617   $134.26   $134.25   $134.30  
  7 purchase totals = $1,264.96       $1,345.3810   $1,345.39   $1,345.35   $1,345.50