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 $201.51   12.738%   $227.1783   $227.18   $227.20   $227.20  
  Purchase #2 $50.34   12.738%   $56.7523   $56.75   $56.75   $56.80  
  Purchase #3 $190.86   7.393%   $204.9703   $204.97   $204.95   $205.00  
  Purchase #4 $64.60   13.826%   $73.5316   $73.53   $73.55   $73.50  
  Purchase #5 $185.92   13.665%   $211.326   $211.33   $211.35   $211.30  
  Purchase #6 $116.94   5.573%   $123.4571   $123.46   $123.45   $123.50  
  Purchase #7 $142.49   6.534%   $151.8003   $151.80   $151.80   $151.80  
  7 purchase totals = $952.66       $1,049.0159   $1,049.02   $1,049.05   $1,049.10