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 $171.93   13.331%   $194.85   $194.85   $194.85   $194.90  
  Purchase #2 $82.29   12.568%   $92.6322   $92.63   $92.65   $92.60  
  Purchase #3 $149.37   10.427%   $164.9448   $164.94   $164.95   $164.90  
  Purchase #4 $214.93   6.537%   $228.98   $228.98   $229.00   $229.00  
  Purchase #5 $121.47   7.668%   $130.7843   $130.78   $130.80   $130.80  
  Purchase #6 $142.34   3.466%   $147.2735   $147.27   $147.25   $147.30  
  Purchase #7 $214.30   5.449%   $225.9772   $225.98   $226.00   $226.00  
  7 purchase totals = $1,096.63       $1,185.4420   $1,185.43   $1,185.50   $1,185.50