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 $172.76   6.861%   $184.6131   $184.61   $184.60   $184.60  
  Purchase #2 $51.67   4.415%   $53.9512   $53.95   $53.95   $54.00  
  Purchase #3 $249.36   9.482%   $273.0043   $273.00   $273.00   $273.00  
  Purchase #4 $247.93   12.424%   $278.7328   $278.73   $278.75   $278.70  
  Purchase #5 $111.71   6.218%   $118.6561   $118.66   $118.65   $118.70  
  Purchase #6 $138.39   10.351%   $152.7147   $152.71   $152.70   $152.70  
  Purchase #7 $178.51   6.708%   $190.4845   $190.48   $190.50   $190.50  
  7 purchase totals = $1,150.33       $1,252.1567   $1,252.14   $1,252.15   $1,252.20