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 $133.52   9.763%   $146.5556   $146.56   $146.55   $146.60  
  Purchase #2 $67.46   10.803%   $74.7477   $74.75   $74.75   $74.70  
  Purchase #3 $161.87   6.134%   $171.7991   $171.80   $171.80   $171.80  
  Purchase #4 $199.68   12.121%   $223.8832   $223.88   $223.90   $223.90  
  Purchase #5 $132.95   9.236%   $145.2293   $145.23   $145.25   $145.20  
  Purchase #6 $218.99   4.232%   $228.2577   $228.26   $228.25   $228.30  
  Purchase #7 $52.87   12.529%   $59.4941   $59.49   $59.50   $59.50  
  7 purchase totals = $967.34       $1,049.9667   $1,049.97   $1,050.00   $1,050.00