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 $70.32   9.127%   $76.7381   $76.74   $76.75   $76.70  
  Purchase #2 $184.91   6.394%   $196.7331   $196.73   $196.75   $196.70  
  Purchase #3 $181.65   7.225%   $194.7742   $194.77   $194.75   $194.80  
  Purchase #4 $211.57   5.859%   $223.9659   $223.97   $223.95   $224.00  
  Purchase #5 $23.72   5.488%   $25.0218   $25.02   $25.00   $25.00  
  Purchase #6 $11.67   10.668%   $12.915   $12.92   $12.90   $12.90  
  Purchase #7 $163.33   9.565%   $178.9525   $178.95   $178.95   $179.00  
  7 purchase totals = $847.17       $909.1006   $909.10   $909.05   $909.10