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 $55.73   13.207%   $63.0903   $63.09   $63.10   $63.10  
  Purchase #2 $189.85   6.669%   $202.5111   $202.51   $202.50   $202.50  
  Purchase #3 $162.47   6.400%   $172.8681   $172.87   $172.85   $172.90  
  Purchase #4 $238.98   5.355%   $251.7774   $251.78   $251.80   $251.80  
  Purchase #5 $147.95   3.381%   $152.9522   $152.95   $152.95   $153.00  
  Purchase #6 $238.92   13.607%   $271.4298   $271.43   $271.45   $271.40  
  Purchase #7 $12.61   13.274%   $14.2839   $14.28   $14.30   $14.30  
  7 purchase totals = $1,046.51       $1,128.9128   $1,128.91   $1,128.95   $1,129.00