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 $56.35   5.336%   $59.3568   $59.36   $59.35   $59.40  
  Purchase #2 $140.87   4.639%   $147.405   $147.41   $147.40   $147.40  
  Purchase #3 $121.53   10.302%   $134.05   $134.05   $134.05   $134.10  
  Purchase #4 $229.37   13.456%   $260.234   $260.23   $260.25   $260.20  
  Purchase #5 $181.96   13.352%   $206.2553   $206.26   $206.25   $206.30  
  Purchase #6 $174.34   4.846%   $182.7885   $182.79   $182.80   $182.80  
  Purchase #7 $64.93   12.171%   $72.8326   $72.83   $72.85   $72.80  
  7 purchase totals = $969.35       $1,062.9222   $1,062.93   $1,062.95   $1,063.00