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 $163.55   10.854%   $181.3017   $181.30   $181.30   $181.30  
  Purchase #2 $202.98   10.713%   $224.7252   $224.73   $224.75   $224.70  
  Purchase #3 $223.35   4.289%   $232.9295   $232.93   $232.95   $232.90  
  Purchase #4 $116.89   5.522%   $123.3447   $123.34   $123.35   $123.30  
  Purchase #5 $91.41   3.850%   $94.9293   $94.93   $94.95   $94.90  
  Purchase #6 $201.55   12.250%   $226.2399   $226.24   $226.25   $226.20  
  Purchase #7 $30.75   13.696%   $34.9615   $34.96   $34.95   $35.00  
  7 purchase totals = $1,030.48       $1,118.4318   $1,118.43   $1,118.50   $1,118.30