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 $183.86   11.417%   $204.8513   $204.85   $204.85   $204.90  
  Purchase #2 $144.78   13.271%   $163.9938   $163.99   $164.00   $164.00  
  Purchase #3 $69.72   11.564%   $77.7824   $77.78   $77.80   $77.80  
  Purchase #4 $87.97   6.598%   $93.7743   $93.77   $93.75   $93.80  
  Purchase #5 $111.29   7.791%   $119.9606   $119.96   $119.95   $120.00  
  Purchase #6 $176.79   7.416%   $189.9007   $189.90   $189.90   $189.90  
  Purchase #7 $151.52   13.217%   $171.5464   $171.55   $171.55   $171.50  
  7 purchase totals = $925.93       $1,021.8095   $1,021.80   $1,021.80   $1,021.90