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 $70.59   4.399%   $73.6953   $73.70   $73.70   $73.70  
  Purchase #2 $230.43   8.553%   $250.1387   $250.14   $250.15   $250.10  
  Purchase #3 $117.28   8.461%   $127.2031   $127.20   $127.20   $127.20  
  Purchase #4 $57.54   5.178%   $60.5194   $60.52   $60.50   $60.50  
  Purchase #5 $222.67   12.713%   $250.978   $250.98   $251.00   $251.00  
  Purchase #6 $196.40   3.524%   $203.3211   $203.32   $203.30   $203.30  
  Purchase #7 $75.35   13.250%   $85.3339   $85.33   $85.35   $85.30  
  7 purchase totals = $970.26       $1,051.1895   $1,051.19   $1,051.20   $1,051.10