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 $165.56   13.460%   $187.8444   $187.84   $187.85   $187.80  
  Purchase #2 $244.62   3.449%   $253.0569   $253.06   $253.05   $253.10  
  Purchase #3 $212.44   7.411%   $228.1839   $228.18   $228.20   $228.20  
  Purchase #4 $63.63   8.488%   $69.0309   $69.03   $69.05   $69.00  
  Purchase #5 $163.78   6.216%   $173.9606   $173.96   $173.95   $174.00  
  Purchase #6 $143.62   4.731%   $150.4147   $150.41   $150.40   $150.40  
  Purchase #7 $87.74   6.513%   $93.4545   $93.45   $93.45   $93.50  
  7 purchase totals = $1,081.39       $1,155.9459   $1,155.93   $1,155.95   $1,156.00