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 $167.58   8.501%   $181.826   $181.83   $181.85   $181.80  
  Purchase #2 $28.61   10.525%   $31.6212   $31.62   $31.60   $31.60  
  Purchase #3 $153.89   10.798%   $170.507   $170.51   $170.50   $170.50  
  Purchase #4 $142.35   3.704%   $147.6226   $147.62   $147.60   $147.60  
  Purchase #5 $194.41   5.439%   $204.984   $204.98   $205.00   $205.00  
  Purchase #6 $119.87   12.132%   $134.4126   $134.41   $134.40   $134.40  
  Purchase #7 $57.71   13.245%   $65.3537   $65.35   $65.35   $65.40  
  7 purchase totals = $864.42       $936.3271   $936.32   $936.30   $936.30