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 $185.87   8.166%   $201.0481   $201.05   $201.05   $201.00  
  Purchase #2 $218.30   9.205%   $238.3945   $238.39   $238.40   $238.40  
  Purchase #3 $84.33   4.168%   $87.8449   $87.84   $87.85   $87.80  
  Purchase #4 $218.35   12.850%   $246.408   $246.41   $246.40   $246.40  
  Purchase #5 $153.73   11.520%   $171.4397   $171.44   $171.45   $171.40  
  Purchase #6 $179.35   6.137%   $190.3567   $190.36   $190.35   $190.40  
  Purchase #7 $13.63   9.592%   $14.9374   $14.94   $14.95   $14.90  
  7 purchase totals = $1,053.56       $1,150.4293   $1,150.43   $1,150.45   $1,150.30