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 $56.68   13.146%   $64.1312   $64.13   $64.15   $64.10  
  Purchase #2 $224.47   8.621%   $243.8216   $243.82   $243.80   $243.80  
  Purchase #3 $202.98   8.218%   $219.6609   $219.66   $219.65   $219.70  
  Purchase #4 $185.93   9.545%   $203.677   $203.68   $203.70   $203.70  
  Purchase #5 $100.74   6.669%   $107.4584   $107.46   $107.45   $107.50  
  Purchase #6 $152.27   5.592%   $160.7849   $160.78   $160.80   $160.80  
  Purchase #7 $32.62   11.595%   $36.4023   $36.40   $36.40   $36.40  
  7 purchase totals = $955.69       $1,035.9363   $1,035.93   $1,035.95   $1,036.00