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 $171.67   13.548%   $194.9279   $194.93   $194.95   $194.90  
  Purchase #2 $239.45   10.245%   $263.9817   $263.98   $264.00   $264.00  
  Purchase #3 $181.33   11.283%   $201.7895   $201.79   $201.80   $201.80  
  Purchase #4 $24.98   11.762%   $27.9181   $27.92   $27.90   $27.90  
  Purchase #5 $231.83   6.868%   $247.7521   $247.75   $247.75   $247.80  
  Purchase #6 $214.68   12.349%   $241.1908   $241.19   $241.20   $241.20  
  Purchase #7 $227.90   12.472%   $256.3237   $256.32   $256.30   $256.30  
  7 purchase totals = $1,291.84       $1,433.8838   $1,433.88   $1,433.90   $1,433.90