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 $162.62   11.826%   $181.8514   $181.85   $181.85   $181.90  
  Purchase #2 $183.35   12.122%   $205.5757   $205.58   $205.60   $205.60  
  Purchase #3 $20.76   12.743%   $23.4054   $23.41   $23.40   $23.40  
  Purchase #4 $134.53   9.414%   $147.1947   $147.19   $147.20   $147.20  
  Purchase #5 $219.98   6.714%   $234.7495   $234.75   $234.75   $234.70  
  Purchase #6 $63.46   3.688%   $65.8004   $65.80   $65.80   $65.80  
  Purchase #7 $146.88   10.533%   $162.3509   $162.35   $162.35   $162.40  
  7 purchase totals = $931.58       $1,020.9280   $1,020.93   $1,020.95   $1,021.00