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 $56.56   12.674%   $63.7284   $63.73   $63.75   $63.70  
  Purchase #2 $163.92   13.782%   $186.5115   $186.51   $186.50   $186.50  
  Purchase #3 $189.96   9.537%   $208.0765   $208.08   $208.10   $208.10  
  Purchase #4 $80.40   13.288%   $91.0836   $91.08   $91.10   $91.10  
  Purchase #5 $183.29   9.199%   $200.1508   $200.15   $200.15   $200.20  
  Purchase #6 $120.33   5.395%   $126.8218   $126.82   $126.80   $126.80  
  Purchase #7 $205.49   6.786%   $219.4346   $219.43   $219.45   $219.40  
  7 purchase totals = $999.95       $1,095.8072   $1,095.80   $1,095.85   $1,095.80